base level buffers and buttresses a model for upstream versus downstream control on fluvial geometry and architecture within sequences abstract the effects of downstream base level control on fluvial architecture and geometry are well explored in several broadly similar sequence stratigraphic models cretaceous dakota group strata u s western interior have characteristics reflecting combined downstream and upstream base level controls that these models cannot address particularly three layers of amalgamated channel belt sandstone within this group thicken and are continuous for distances 300 km along dip that stretch the reasonable lengths for which these models are intended to apply as well architecture in up dip reaches records repeated valley scale cut and fill cycles this contrasts with equivalent strata down dip which record channel scale lateral migration with no such valley scale cycles apparent we here introduce the concept of buffers and buttresses to address these observations we assume that river longitudinal profiles are each anchored down dip to some physical barrier e g the sea strand etc that we refer to as a buttress buttress shift is considered the primary downstream control on base level profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high frequency variability in upstream base level controls e g discharge etc all these potential profiles however are bounded above by the profile of highest possible aggradation and below by the profile of maximum possible incision these upper and lower profiles are buffers and they envelop the available fluvial preservation space thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance dakota valley scale surfaces record repeated cut and fill cycles driven by up dip controls and are confined between thick stable buffers equivalent strata down dip record lateral reworking within a thinner channel scale buffer zone that was positioned by downstream controls regression exposed slopes similar to the buffer zone thus buffers were stable for long distances and durations this prompted dip extensive lateral reworking of strata into upstream valley scale and downstream channel scale sheets buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs downstream base level controls on geometry and architecture the model lends general insights into dip oriented variations in fluvial architecture production of sheet vs lens geometry total preservation volumes for fluvial systems and variations in these factors related to contrasting climatic conditions and basin physiography the model can be amended to existing sequence stratigraphic approaches in order to capture dip oriented variations in sequence architecture

geomorphic thresholds and complex response of fluvial systems some implications for sequence stratigraphy first generation sequence stratigraphic models have dealt in a very rudimentary fashion with the response of fluvial systems to eustasy a major element of presently accepted models is that rivers incise when sea level falls and aggrade during the ensuing rise well established geomorphic principles state that fluvial systems are complex process response systems that can adjust to internal and external changes in other ways besides incision and aggradation by modifying their stream patterns and channel geometries application of geomorphic principles to sequence stratigraphic models results in the following observations during eustatic lowstands rivers may adjust to lowered base levels and changes in slope by modifying channel patterns therefore not all lowstands produce type 1 sequence boundaries type 1 sequence boundaries characterized by fluvial valley incision are more likely to develop when sea level drops below the shelf slope break resulting in topological relief near the strandline in which headwardly eroding knickpoints form rates of eustatic change although rapid in a geological context are sufficiently low that geomorphic systems can easily maintain their equilibrium during eustatic changes and migrate back and forth across the shelf without major modifications finally und r conditions of relatively static sea level sequences and parasequences of the same scale in time and space as those which form during eustatic change can be deposited as the result of purely intrinsic causes and responses of a fluvial system in general eustasy controls the location of deposition and erosion but the resultant stratal geometry is controlled by sediment supply and processes acting on the sediments as the shoreline moves across the shelf in response to eustasy

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea shallow seismic profiles and borehole data revealed active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea the ridges consist of relatively clean well sorted sands with fairly uniform sequences the microfossil assemblage exhibits a high diversity including both euryhaline and stenohaline species the ridges are huge elongated sand bodies several kilometres wide 10 60 km long and up to 20 m thick and occur in groups with a spacing of several to 10 km normally they are parallel with each other extending in the direction of the tidal currents the field of tidal sand ridges on the east china sea shelf covers an area of 57 000 km2 tidal sand ridges in the east china sea and the southern yellow sea were formed in estuarine and shallow shelf environments where strong tidal currents reworked transported and redeposited large amounts of relict sands from older deltaic and fluvial sediments the development of tidal sand ridges in estuary mouth areas is accompanied by a net sand transport from the shelf into the estuary the evolution of tidal sand ridges is closely related to transgressions active tidal sand ridges are formed during sea level rises they show distinct morphology and active migrations in a lateral as well as in a landward direction they are generally in equilibrium with present day tidal processes and their distribution patterns are related to the flow field of the tidal currents as the sea level rises further these tidal sand ridges become moribund sand bodies with less distinct morphologies their upper surfaces are covered by a thin calcareous rich layer with very high contents of foraminifera tests reflecting a submarine hiatus condition on the shelf during the highstand period during the subsequent steady fall in sea level tidal sand ridges are often buried by fine grained shelf and prodelta sediments they have therefore a good chance of being preserved in stratigraphic records the sequential buildup during a sea level rise tr tract and a subsequent sea level fall hs and ls tract would consist of estuarine channel and tidal flat facies tidal sand ridge facies shelf mud facies delta facies and fluvial facies in an ascending order tidally dominated estuary conditions may also occur when a major distributary is abandoned such as at the northern branch of the modern changjiang river mouth where the accumulation of sand from an abandoned delta lobe and the development of tidal sand ridges have been observed the observed features have important implications for the subsurface recognition of fossil tidal sand ridges for the reconstruction of the regional palaeogeography and transgressional history and for the prediction of potential reservoir sandstones

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

evidence for sea level and monsoonally driven variations in terrigenous input to the northern east china sea during the last 24 3 ka geochemical and sedimentological analyses of core pc 1 recovered from the northern east china sea ecs provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24 3 ka based on high resolution multiproxy records our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ecs dominance of terrigenous material along with relatively light globigerinoides ruber 18o indicates that the last glacial maximum lgm lowstand of sea level has occurred during the period 21 5 19 6 ka not suggesting an early slow rise but supporting the conventional lgm age of 21 ka this lgm lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse mwp which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19 6 to 18 9 ka mwp 1a is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of g ruber 18o at 15 3 14 8 ka given the considerable age uncertainties of deglacial marine radiocarbon samples a slightly increasing input of terrigenous matter is noted after 13 4 ka potentially pointing to a sea level fall following the inter allerod cooling period which was seldom reported previously although mwp 1b did not leave robust signatures in terrigenous input it is explicitly captured by the heavy 18o of g ruber and decline in mean grain size at 11 5 10 9 ka mwp 1c probably occurred in a broad millennial interval with multiple peaks which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9 7 9 3 and 9 1 ka respectively during the late holocene the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine derived organic matter after 5 5 ka

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

paleosols and associated channel belt sand bodies from a continuously subsiding late quaternary system po basin italy new insights into continental sequence stratigraphy previous sequence stratigraphic work has emphasized the key role of paleosols and associated sand dominated fluvial bodies as key features for interpreting alluvial architecture the temporal resolution of the ancient record is however insufficient to fully explain the complex relationship between soil formation and the evolution of fluvial systems under changing sea level and climate conditions in this paper we present a detailed record of paleosol channel belt relationships reconstructed from the subsurface of a rapidly subsiding region po plain italy that spans almost all of the last glacial interglacial cycle 120 k y the studied succession preserves a systematic bipartite zonation into a thick paleosol bearing segment close to the basin margin and a sand dominated interval with vertically amalgamated channel belts in an axial position individual paleosols are weakly developed and represent key stratigraphic markers that can be traced basinwide into adjacent essentially contemporaneous unconfined channel belt deposits unlike conventional models of late quaternary alluvial coastal plain systems no persistent incised valley was established in the po system during the last glacial interglacial cycle continuous accommodation was the key depositional control on alluvial stratigraphy during the prolonged 90 k y phase of late pleistocene sea level fall which led to the deposition of a thick dominantly aggradational alluvial succession the development of shallowly incised short lived valley systems took place only at the transition to glacial stages associated with substantial sea level drop marine oxygen isotope stage mis 3 2 transition and possibly mis 5 4 transition this study shows that in rapidly subsiding settings with high rates of sedimentation incised valley systems may be replaced by aggradationally stacked essentially nonincised fluvial bodies in these cases overbank packages bounded by immature paleosols represent the most likely alternative to the highly weathered interfluve paleosol predicted by classic sequence stratigraphic models fourth order sequence boundaries and lower rank erosional surfaces may be easily confused at the 100 k y scale and transgressive surfaces defining the onset of retrogradation may become the most readily identifiable sequence stratigraphic surfaces

stratigraphy of late quaternary deposits using high resolution seismic profile in the southeastern yellow sea abstract high resolution chirp and sparker system seismic profiles were analyzed to investigate the sequence stratigraphy of late quaternary deposits in the southeastern yellow sea approximately 1560 line km data of chirp and sparker profiles were acquired together with 11 piston cores two previous long drill cores ysdp 102 and 103 were used for comparison with seismic data high resolution seismic profiles image the holocene mud deposits and the complex sedimentary structure in this area sequence analysis of high resolution seismic profiles reveals that the shelf deposits form a succession of high frequency five order sequences consisting of one depositional sequence developed during the late quaternary the depositional sequence includes five sedimentary units each with different seismic facies and geometry 1 incised channel fill and lowstand deltaic wedge unit sy1 2 sand ridges unit sy2 3 estuarine deltaic mud unit sy3 4 redeposited mud unit sy4 and 5 recent distal mud unit sy5 based on the interpretation of high resolution seismic records and correlation with the ysdp 102 103 long cores and piston cores late quaternary deposits in the southeastern yellow sea consists of a set of the lowstand unit sy1 early transgressive unit sy2 middle transgressive unit sy3 late transgressive unit sy4 and highstand systems tract unit sy5 formed since the last glacial period the rather unusual stratigraphic architecture including three systems tracts is largely controlled by the postglacial sea level changes and regionally circulation pattern associated with sediment erosion and redeposition the results of this study present firstly clear seismic evidence that the southeastern yellow sea mud belt seysm can be divided into three stratigraphic units units sy3 sy4 and sy5 bounded by distinct bounding surfaces

structure chemistry and origins of gypsum crusts in southern tunisia and the central namib desert gypsum crusts are broadly defined as accumulations at or within about 10 m of the land surface from 0 10m to 5 0 m thick containing more than 15 by weight gypsum caso4 2h2o and at least 5 0 by weight more gypsum than the underlying bedrock the deposits are often but not invariably consolidated owing to cementation by gypsum the crusts are found in many of the world s deserts where mean monthly potential evaporation exceeds mean monthly precipitation throughout the year using structural fabric and textural criteria three main types of crust may be distinguished 1 bedded crusts found either at or beneath the land surface which are made up of discrete horizontal strata up to 0 10 m thick each showing a gradation in gypsum crystal size from less than 50 m at the top to more than 0 50 mm at the base 2 subsurface crusts of which there are two forms one made up of large lenticular crystals up to 0 50 m in diameter the desert rose crusts and the other a mesocrystalline form with gypsum crystals up to about 1 0 mm in diameter and 3 surface crusts which are subdivided into columnar powdery and cobble forms all of which are made up of predominantly alabastrine gypsum crystallites less than 50 m in diameter in southern tunisia and the central namib desert bedded crusts are found around ephemeral lakes and lagoons they are characterized by size graded beds gypsum contents of 50 80 by weight and comparatively high concentrations of sodium potassium magnesium and iron they are interpreted as shallow water evaporites which accumulate when saline pools evaporate to dryness desert rose crusts or croutes de nappe generally contain 50 70 by weight gypsum and have higher sodium concentrations than the second subsurface form texturally they are characterized by poikilitic inclusion of clastic material within large lenticular crystals they are interpreted as hydromorphic accretions which precipitate in host sediments at near surface water tables through the evaporation of groundwater the second form of subsurface crust the mesocrystalline often occurs in close association with the various surface forms unlike the hydromorphic crusts they are not restricted to low lying terrain they are characterized by gypsum contents reaching 90 by weight and have a close chemical and textural similarity to columnar surface crusts this mesocrystalline form represents an illuvial accumulation the surface forms excluding the bedded crusts are exhumed examples at various stages of solutional degradation subsurface precipitation of gypsum from meteoric waters containing salts leached from the surface results in displacive gypsum accumulation in the soil zone in southern tunisia the gypsum is derived from sand and dust deflated from evaporitic basins in the central namib salts dissolved in fog water are the most likely source where other salts are present differential leaching may form two tiered crusts calcrete gypsum or gypsum halite if rainfall is sufficient to mobilize the less soluble salt yet insufficient to flush the more soluble gypsum crust genesis is restricted to arid environments and if their susceptibility to post depositional alteration is acknowledged they can provide valuable palaeoclimatic indicators

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

high ground water levels and dune development in central australia tl dates from gypsum and quartz dunes around lake lewis napperby northern territory abstract an episode of high lake levels prior to the last maximum glaciation has been identified at many localities in wastern australia similar events have been recognized at playa lakes in central australia where gypsum dunes along playa margins formed during one or more episodes of high groundwater discharge with a large influx of calcium sulphate at lake lewis exposures at two islands show similar sediment sequences three pedogenic gypcrete layers interbedded with aeolian quartz and gypsum sand horizons form three units within gypsum dunes up to 7 m high the lowest unit has cliffed edges buried by the upper units indicating a significant time break four tl dates coarse grained quartz show that this lowest unit was deposited at or before 70 80 ka the middle unit of mixed gypsum and quartz sand capped by gypcrete represents the major phase of gypsum dune formation and 6 tl dates range from 33 to 46 ka with overlapping error bars these are slightly younger but statistically similar to tl dates from 39 to 59 ka of the shoreline gypsum dune at lake amadeus in the same region the top unit of the two islands up to 1 m thick has not yet been well dated one date is inconsistent with the well dated middle layer below possibly because of incomplete bleaching and has been rejected the other date 17 5 ka is much younger which possibly indicates a minor and local reactivation of old gypsum sediments at the lake margin there are quartz dunes overlying the gypsum dunes and a buried aeolian quartz sand layer occurs in a lake margin terrace these represent reactivation of the regional quartz dune field after the major gypsum dune formation two consistent tl dates 21 4 ka and 23 6 ka indicate that regional dunes were active at about the time of the last glacial maximum

evolution of the coastal depositional systems of the changjiang yangtze river in response to late pleistocene holocene sea level changes abstract the paleo changjiang yangtze incised valley fills approximately 80 90 m thick provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late pleistocene holocene sea level fluctuations on time scales of 103 to 104 years the sedimentary facies of the incised valley fills record three main depositional systems fluvial tide dominated estuary and tide dominated delta radiocarbon ages for the incised valley fills suggest that these depositional systems developed before about 11 ka between 11 and 8 ka and after approximately 8 ka respectively by applying sequence stratigraphic concepts the evolution of the depositional systems can be divided into three systems tracts a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst sea level changes on a 104 year time scale controlled the basic architecture of the sequence of the incised valley fill on the other hand sea level changes on a millennial time scale affected the stacking pattern of the systems tracts in particular the continuous sea level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the tst which is characterized by a combination of aggradation and backstepping the aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level and a very rapid sea level rise around 12 and 10 ka caused the system to migrate abruptly landward unlike the transgressive estuarine phase the stacking pattern of the regressive tide dominated delta hst which developed within the almost filled incised valley and on the surrounding interfluve zones was characterized by seaward progradation with clinoform architecture it was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea level rise and was followed by a progradational phase after the highest sea level about 6 ka

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

aeolian responses to climate variability during the past century on mesquite lake playa mojave desert abstract the erosion and deposition of sediments by wind from 1901 to 2013 have created large changes in surface features of mesquite lake playa in the mojave desert the decadal scale recurrence of sand sheet development migration and merging with older dunes appears related to decadal climatic changes of drought and wetness as recorded in the precipitation history of the mojave desert complemented by modeled soil moisture index values historical aerial photographs repeat land photographs and satellite images document the presence and northward migration of a mid 20th century sand sheet that formed during a severe regional drought that coincided with a multi decadal cool phase of the pacific decadal oscillation pdo the sand sheet slowly eroded during the wetter conditions of the subsequent pdo warm phase 1977 1998 due to a lack of added sediment sand cohesion gradually increased in the sand sheet by seasonal additions of salt and clay and by re precipitation of gypsum which resulted in the wind carving of yardangs in the receding sand sheet smaller yardangs were aerodynamically shaped from coppice dunes with salt clay crusts and larger yardangs were carved along the walls and floor of trough blowouts evidence of a 19th century cycle of sand sheet formation and erosion is indicated by remnants of yardangs photographed in 1901 and 1916 that were found buried in the mid 20th century sand sheet three years of erosion measurements on the playa yardangs and sand sheets document relatively rapid wind erosion the playa has lowered 20 to 40 cm since the mid 20th century and a shallow deflation basin has developed since 1999 annually 5 10 cm of surface sediment was removed from yardang flanks by a combination of wind abrasion deflation and mass movement the most effective erosional processes are wind stripping of thin crusts that form on the yardang surfaces after rain events and the slumping of sediment blocks from yardang flanks these wind eroded landforms persist several decades to a century before eroding away or being buried by younger sands on mesquite lake playa the climatic history of alternating pdo phases of multi decadal drought and wetness is recorded twice by the presence of yardangs formed nearly a century apart

aeolian landscapes in central australia gypsiferous and quartz dune environments from lake amadeus there are two different dune systems in central australia regional quartz dunefields and transverse gypsiferous dunes associated with playa lakes these two systems especially gypsiferous dunes at lake amadeus the largest playa in central australia provide a sedimentary geomorphological and environmental history of the region during the late quaternary the gypsifierous dunes consist of a surficial gypcrete overlying an aeolian sediment sequence below a mixture of gypsum sand and quartz sand no clay pellets have been found in the dune sequence in significant contrast to the gypsiferous clay dunes in other parts of australia three possible models of the environmental controls of gypsiferous dune formation are discussed the most plausible one suggests simultaneous gypsum precipitation and deflation sandsized gypsum was precipitated in a groundwater seepage zone around the playa margin during seasonally high water tables and these crystals were deflated onto land during dry intervals forming the marginal gypsiferous dunes these processes require conditions of high regional water table strong climatic seasonality and probably a windier and overall wetter climate at least two separate gypsiferous duneforming episodes can be recognized the age of formation of the younger one has been dated by thermoluminescence at 44 54 ka the gypcrete crust capping the dunes is characterized by intergrown microcrystalline gypsum crystals showing evidence of leaching dissolution and recrystallization it is interpreted as a pedogenic product formed during a stable period after accumulation of the gypsiferous dune after the construction of the younger gypsiferous dune there was a major episode of activation of regional quartz dunefields which formed thick quartz sand mantles overlying gypsiferous dunes on both playa margins and the dune islands within the playa an equivalent aeolian sand layer was deposited within the playa soil structures in this unit indicate that the sand sheet over the playa was later colonized by vegetation activation of the regional dunefields suggests a major period of dry climate which although not dated may correlate with the last glacial maximum identified as a period of maximum aridity from 25 to 18 ka at other sites in australia

devonian fluviodeltaic sedimentation in hong kong abstract twenty three distinct sedimentary facies have been distinguished in the devonian bluff head formation exposed around the tolo channel area of northeastern hong kong these facies have been combined into five facies associations channel aeolian sheetflood deltaic and palaeosol with the bulk of the formation belonging to the channel association the lower part of the bluff head formation around plover cove consists of upwards coarsening cycles each typically 3 m thick the basal parts of some cycles contain distinctive marine fossils of early to middle devonian age sedimentation occurred on a marine influenced delta plain with eustatic sea level rises controlling cycle development the middle and upper parts of the formation contrast strongly with the lower part and show a distinct change to alluvial plain sedimentation upward fining cycles each approximately 40 m thick comprise basal multistorey braided conglomerate filled channel deposits at the base passing upwards into finer grained sheetflood aeolian and channel sandstones at the top palaeosols in the higher parts of the cycles indicate periods of non deposition under semi arid climatic conditions these cycles represent repeated abandonments of the fluvial system which we suggest were controlled by tectonic pulses

enormous ganges brahmaputra sediment discharge during strengthened early holocene monsoon rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development however little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes in this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early holocene monsoon development of the ganges brahmaputra river delta began ca 11000 yr b p when rising sea level flooded the bengal basin thereby trapping most of the river s discharge on the inner margin chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin which provide a minimum estimate of the river s past sediment load results reveal that 5 1012 m3 of sediment was stored in the bengal basin from ca 11000 to 7000 yr b p which corresponds to a mean load of 2 3 109 t yr in comparison modern sediment load of the ganges brahmaputra is 1 109 t yr ranking it first among the world s rivers and underscoring the significance of a two fold increase sustained over 4 k y furthermore the timing of immense discharge in the early holocene strongly suggests its relation to a stronger than present southwest monsoon in south asia similar patterns of high monsoon related sediment discharge have been noted throughout the tropics and subtropics suggesting a widespread fluviosedimentary response the potential magnitude of which is showcased by the ganges brahmaputra system

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the east china sea abstract paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the east china sea ecs undertaken in 1996 the geophysical data are correlated with a borehole situated on the outer shelf obtained by shanghai marine geology bureau indicating that six seismic units have been preserved since oxygen isotope stage 6 including four regressive transgressive cycles seismic units u2 u3 u4 u5 u6 and u7 are interpreted to correspond respectively to oxygen isotope stages 1 3 5 and 6 implying that sediment partitioning and sequence architecture in the ecs have been controlled by glacio eustasy and global climate changes alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ecs most of the cold environment strata which formed on the outer shelf during oxygen isotope stages 2 and 4 are too thin to be recognized on sig 600j because of resolution but corresponding erosion surfaces exist seismic unit u7 is widespread over the shelf extending to the continental edge and showing little variation in thickness as the regression was pronounced and lasted a long time thus u7 can be used as a marker layer for correlation of quaternary strata on the shelf of the ecs post glacial transgression is obvious in the ecs marine strata with varied thickness were developed in the shallow sea of the inner shelf thinning toward the outer shelf the continental shelf of the ecs has been influenced by pacific tide wave systems for a long time forming tidal sand ridge sequences developed during transgressions corresponding to oxygen isotope stages 7 or 9 5 3 and 1

palaeochannels on the north china plain palaeoriver geomorphology abstract variations in the geomorphology of the north china plain are related to differences between river deposits the river deposits from different periods form the various geomorphological features different combinations of palaeochannels form different geomorphological regions different kinds of palaeochannels form different kinds of micro geomorphology during the early glaciation of the late pleistocene the river deposits formed piedmont plains and floodplains by the early holocene the rivers had cut the piedmonts into dissected valleys and deposited alluvial fans at the front edge of the piedmonts to form alluvial plains below by the middle holocene lake sediments covered the alluvial plains and filled in the dissected valleys of the piedmont plains by the late holocene rivers dissected the piedmonts again to form dissected valleys and deposited alluvial fans in the lower reaches to form alluvial plains and deltas at the river mouths

reconstructing last glacial maximum and younger dryas paleolandscapes through subsurface paleosol stratigraphy an example from the po coastal plain italy abstract paleosols are commonly used to reconstruct ancient landscapes and past environmental conditions through identification and subsurface mapping of two pedogenically modified surfaces formed at the onset of the last glacial maximum lgm and during the younger dryas yd cold event respectively and based on their lateral correlation with coeval channel belt sand bodies we assessed the geomorphic processes affecting the po coastal plain during the late pleistocene 30 11 5 cal ky bp the 3d reconstruction of the lgm and yd paleosurfaces provides insight into the paleolandscapes that developed in the po alluvial plain at the transitions between warm and cold climate periods the lgm paleosol records a stratigraphic hiatus of approximately 5 kyr 29 24 cal ky bp whereas the development of the yd paleosol was associated with a climatic episode of significantly shorter duration both paleosols dissected by apennine rivers flowing from the south dip towards the north east where they are replaced by fluvial channel belts fed by the po river the lgm channel belt sand body reflects the protracted lateral migration of the po river at the onset of the glacial maximum it is wider 24 km and thicker 15 m of the fluvial sand body formed during the yd the northern margin of lgm po channel belt deposits was not encountered in the study area in contrast a spatially restricted paleosol identified in the north at the same elevation as the southern plateau may represent local expression of the alpine interfluve during the yd event this study highlights how 3d mapping of regionally extensive weakly developed paleosols can be used to assess the geomorphic response of an alluvial system to rapid climate change

late quaternary landscapes in central australia sedimentary history and palaeoecology of puritjarra rock shelter puritjarra rock shelter provides a long record of late quaternary vegetation in the australian arid zone analysis of the sedimentary history of this rock shelter is combined with reanalysis of charcoal and phytolith records to provide a first order picture of changing landscapes in western central australia these show a landscape responding to increasing aridity from 45 ka with deflation of clay rich red palaeosols 45 ka and sharp declines in grassland and other vegetation at 40 36 ka and at the beginning of the last glacial maximum lgm 24 ka vegetation in the catchment of the rock shelter recovered after 15 ka with expansion of both acacia woodland and spinifex grasslands registering stronger summer rainfall in the interior of the continent by 8 3 ka re vegetation of local palaeosols and dunes had choked off sediment supply to the rock shelter and the character of the sediments changed abruptly poaceae values peaked at 5 8 ka suggesting the early mid holocene climatic optimum in central australia is bracketed between 8 3 and 5 8 ka local vegetation was disrupted in the late holocene with a sharp decline in poaceae at 3 8 ka coinciding with an abrupt intensification of enso local grasslands recovered over the next two millennia and by 1 5 ka the modern vegetation appears to have become established copyright 2009 john wiley sons ltd

parabolic halite dunes on the salar de uyuni bolivia abstract palaeoenvironmental interpretation in desert and evaporitic sediments is often ambiguous consequently the recognition of primary sedimentary structures that indicate subaerial exposure or shallow marine conditions are therefore of crucial importance when interpreting marginal sedimentary evaporite facies parabolic halite dunes described here for the first time are observed on the salt crust of the largest salt flat in the world the salar de uyuni in bolivia the halite dunes are relatively small 0 7 1 3 m in width and length well defined lobate to hemicyclic parabolic dunes and are formed directly on the salt crust a model describing the formation and migration of the dunes in relation to brine level and climatic conditions is presented

radiocarbon dates from the east china sea and their geological implications abstract radiocarbon analysis plays an important role in studying the quaternary geologic history of the east china sea more than 200 14 c dates have been published in various chinese publications the continental shelf of the east china sea is one of the few large continental shelves in the world many low lying flats and deltaic plains lie along the coast making it a favorable site for sea level studies radiocarbon data from neolithic sites chenier ramparts peaty deposits and submarine sediments converge to suggest that oscillations of sea level have occurred they also suggest that the lowest glacial sea levels probably occurred between 22 000 and 19 000 yr b p calculation of the volume of the yangtze river delta together with 14 c dates indicates that more than 89 of the solid particles carried by the river were deposited in the delta due to the sedimentary load the crust beneath the delta has subsided isostatically and tilted seaward marine shells provide many acceptable 14 c dates but because they are easily transported most samples from the continental shelf cannot be directly related to the history of sea level changes

reappraisal of the sequence boundary in time and space case and considerations for an su subaerial unconformity that is not a sediment bypass surface a time barrier or an unconformity abstract the sequence bounding unconformity bears the key defining traits of being a surface separating younger from older strata along which there is evidence of subaerial erosional truncation or subaerial exposure with a significant hiatus indicated van wagoner et al 1988 this subaerial component of sequence boundaries subaerial unconformity su is also broadly considered to form as a topographic surface of sediment bypass carved during relative sea level fall and buried by backfilling during relative sea level rise accordingly the su is commonly presumed to record an approximate time barrier which separates older from younger strata along its full length in this paper we show that regional composite scour rcs surfaces that are traditionally mapped as an integral component of the su were never a single subaerial topographic surface characterized by sediment bypass are not unconformities do not record an effective time barrier and form diachronously at the channel belt scale over the entire fall to rise of a base level cycle these rcs surfaces and by inference the su surfaces they comprise thus do not fully fit key defining characteristics embodied in the conceptual sequence boundary flume observations and field data show that the rcs is buried by fluvial sediment simultaneously as it is scoured accordingly the rcs is perennially covered with stored sediment during formation is only exposed as a subaerial topographic surface at the local place and time where it is undergoing active growth and forms over the duration of local marine drainage during a relative sea level cycle this cut and cover model differs greatly from more established bypass models which assume that the rcs was roughly sediment free and subaerially exposed for long durations of incision during regression and thus preserves a significant depositional hiatus upon later burial instead the rcs may commonly and locally record a hiatus more typical of a facies bounding diastem without a lacuna significantly greater than that of surfaces within the strata it binds fragments of fluvial strata may commonly and sporadically be preserved above the rcs that are older than underlying marine units overrun by this surface consequently the rcs is not an effective time barrier lateral planation by migrating and avulsing channels as the rcs expands laterally after nucleation can place younger fluvial strata over much older units which means that this surface is also composite and highly diachronous laterally at the scale of channel belts the cut and cover model has additional implications not captured by the bypass model first significant sediments may be stored within fluvial strata above the rcs during regression that are not available for contemporary falling stage and lowstand marine shorelines this can result in marine sediment starvation particularly of the sand fraction and in extreme cases can result in sand autodetachment and an absence of regressive marine reservoir sandstones second cutting of the rcs co generates a suprafluvial surface above the covering fluvial strata during regression that may be used as a mappable proxy for the conceptual maximum regressive surface mrs the mrs may be raised above this surface locally by low accommodation aggradation during lowstand normal regression but in either case preserves an approximate time line where not reworked during later transgression third valley development across the rcs does not exclusively form by landward knickpoint growth and may include complexly formed and potentially cross cutting buffer valleys su valley incision can be divided into four modes which include denudation structural buttress and buffer valley components which may work together locally and tend to have variable importance along the shore to hinterland profile although the rcs is not a good rock proxy for the conceptual sequence boundary it remains a very mappable surface which may separate facies of potentially very different origin and reservoir quality the rcs is also inseparable from the su and typically the only terrestrial erosional surface of extent in most short duration sequences its nullification as a sequence boundary would mean abandonment of depositional sequence stratigraphy as a correlation and interpretive tool within these sections an alternative to abandonment of the su as a sequence boundary is to loosen the definition of a sequence boundary to a discrete surface of erosional truncation carved landward of contemporary shorelines that is traceable beyond the scale of a single valley or comparable local system and its correlative surfaces of conformity and or non deposition and continue its use as before

the late pleistocene evolution of palaeo megalake bungunnia southeastern australia a sedimentary record of fluctuating lake dynamics climate change and the formation of the modern murray river abstract the ephemeral lacustrine carbonates of the bungunnia limestone deposited in palaeo megalake bungunnia preserve a detailed record of pleistocene palaeoenvironmental and palaeoclimatic change in southeastern australia five distinct lake shorelines lake levels 0 4 are visible on digital elevation models ranging in elevation from around 70 m to 30 m above sea level the bungunnia limestone is preserved on the three lowest terraces ranging over 20 m in elevation lake levels 2 4 on the two higher of these terraces bungunnia limestone contains ooids and stromatolites and is calcite and aragonite dominated whereas on the lower terrace level bungunnia limestone is dolomite gypsum and magnesite dominated and preserves tepee structures and mud cracks thus lacustrine conditions are interpreted to have become increasingly saline and evaporitic over time reflecting an overall trend to more arid climatic regimes the highest lake level level 0 at around 70 m above sea level appears to relate to a period of significantly increased rainfall that allowed the lake to overflow for the first time marking the initiation of the modern murray river subsequently the lake fluctuated between 1 a steady state open lake system where water was overflowing across the padthaway high spillpoint and active gorge cutting was proceeding and 2 a closed lake system with no overflow that resulted in carbonate precipitating conditions during 1 shoreline erosion was occurring within the basin providing the terraces on which the bungunnia limestone carbonates were deposited during 2 in this 1 is likely to correspond with significantly wetter late pleistocene interglacial and 2 with arid glacial conditions the formation of the modern murray river and the demise of palaeo megalake bungunnia were therefore consequences of a combination of gorge cutting and increasing aridity resulting from interglacial glacial climate oscillation superimposed on significant overall climatic change

palaeochannels on the north china plain types and distributions abstract a palaeochannel is the geomorphological expression of an abandoned river channel caused by either human or natural factors it is expressed by topographic form sediment and hydrogeomorphology and may be visible on air photos and satellite images the palaeochannels of the north china plain can be classified as surface palaeochannels and shallow buried palaeochannels the surface palaeochannels can be further divided into crevasse channels palaeoriver channels trough shaped palaeochannels and strip shaped elevated palaeochannels palaeochannel zones may include combinations of these types the distribution of the palaeochannels in the north china plain is radial on the piedmont plain parallel on the floodplain and crown shaped on the coastal plain

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

mineralogical maturity in dunefields of north america africa and australia studies of dunefields in central and western north america show that mineralogical maturity can provide new insights into the origin and evolution of aeolian sand bodies many of the world s great sand seas in africa asia and australia are quartzdominated and thus can be considered to be mineralogically mature the algodones california and parker arizona dunes in the southwestern united states are also mature but have inherited a high degree of mineralogical maturity from quartz rich sedimentary rocks drained by the colorado river in libya sediments of the zallaf sand sea which are almost pure quartz may have originated in a similar fashion the fort morgan colorado and casper wyoming dunefields in the central great plains of north america and the namib sand sea of southern africa have an intermediate degree of mineralogical maturity because their sources are large rivers that drained both unweathered plutonic and metamorphic rocks and mature sedimentary rocks mojave desert dunefields in the southwestern united states are quite immature because they are in basins adjacent to plutonic rocks that were their sources other dunefields in the great plains of north america those in nebraska and texas are more mature than any possible source sediments and therefore reflect mineralogical evolution over time such changes in composition can occur because of either of two opposing long term states of the dunefield in one state dunes are stable for long periods of time and chemical weathering depletes feldspars and other weatherable minerals in the sediment body in the other state which is most likely for the great plains abrasion and ballistic impacts deplete the carbonate minerals and feldspars because the dunes are active for longer periods than they are stable d 2003 elsevier b v all rights reserved

drainage area and incised valley fills in texas rivers a potential explanation abstract the largest rivers draining to the gulf of mexico in texas are at more advanced stages of valley filling than rivers with smaller drainage areas with corresponding differences in alluvial morphology and architecture and avulsion style this seems to imply that the larger fluvial systems either produce more sediment relative to the accommodation space in the alluvial valleys or that they have undergone longer periods of valley aggradation however it is not clear that either of these is the case this paper presents a theoretical analysis showing that fluvial systems with larger drainage areas can produce more advanced stages of infilling than those with smaller drainage areas but with identical histories and sediment production per unit area due to the nature of the scaling relationships between drainage basin area and incised valley size and between basin area and sediment yield data for rivers in the region shows a strong linear relationship between valley width and drainage area the nonlinear relationship between drainage area and proportion of the incised valley filled is somewhat weaker but still significant and major deviations are readily explained in terms of local inherited morphology or tectonic features results show that major differences in the degree or stage of valley filling could occur due to differences in drainage basin size alone this indicates caution in interpreting incised valley fills of drainage basins of different sizes in terms of sediment supply

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

formation of the yangtze shoal in response to the post glacial transgression of the paleo yangtze changjiang estuary china abstract the yangtze shoal lies east of the yangtze changjiang river estuary china at water depths of 25 55 m and is one of the largest subaqueous sheet like sand banks in the world previous studies have not reached a consensus regarding its origin and timing of formation mainly due to the scarcity of coring and high resolution seismic profiling in the shoal we recovered a 70 20 m long sediment core cre 1402 through the sand shoal and acquired 1586 km of high resolution shallow seismic profiles across the estuary and shoal we conducted systematic analyses of the core including its sedimentary characteristics down core changes in benthic foraminiferal assemblages and 14c and optically stimulated luminescence osl dating we also analyzed the seismic stratigraphy and integrated these results with data from other previously well studied cores onshore and offshore of the yangtze river mouth our results indicate that the stratigraphic architecture in the paleo yangtze estuary i e the area from the present day delta plain to the subaqueous delta and yangtze shoal was controlled mainly by changes in sea level during the post glacial transgression the post 14 ka sedimentary successions in the paleo estuary rest unconformably on fluvial or coastal deposits that formed mainly before mis 1 and are separated by three distinctive bounding surfaces corresponding to mwp 1a mwp 1b or the rapid sea level rise at ca 11 5 ka shortly after the younger dryas cold period and the 8 2 ka event respectively and the maximum marine flooding surface mfs the depositional unit of the yangtze shoal ranges in thickness from 6 to 32 m the shoal exhibits large scale sw dipping generally 0 5 2 foresets with local cross cutting of foresets which are composed mainly of very fine to medium grained sands the shoal is underlain by muddy intertidal to subtidal flat deposits that formed during the younger dryas with an erosional surface corresponding to mwp 1b or the rapid sea level rise at ca 11 5 ka between these and the shoal deposits the yangtze shoal came into being mainly between ca 11 5 and 7 0 ka in the form of tidal sand ridges actively moving southwestwards under intense and reciprocal tidal currents on a tidal shelf the tidal sand ridges have evolved into sheet like tidal sand banks with relatively low relief as a result of tidal remobilization under rotary tidal currents since ca 7 0 ka when the mfs formed therefore the yangtze shoal can be considered to comprise quasi active tidal sand banks

mineralogical and isotopic evidence for the sediment provenance of the western south yellow sea since mis 3 and implications for paleoenvironmental evolution abstract changing sediment provenance and related paleoenvironmental evolution since marine isotope stages mis 3 have been investigated based on accelerator mass spectrometry ams 14c and optically stimulated luminescence osl dating of core csdp 01 recovered from the western south yellow sea sys based on our results sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes sea level fluctuations determined the accommodation space in the shelf area while the monsoonal climate controlled the sediment supply capacity from river to sea mineral and sr nd isotopic records reveal the major contribution of the paleo changjiang river yangtze river to the study core area during the early mid mis 3 which likely defined the northern limit of the paleo changjiang delta at that time high sediment supply and limited accommodation space led to the development of sediment fed systems on the sys shelf resulting in a high preservation potential for thick stacking and overlapping deltaic sediments along with deltaic progradation core sediment provenance gradually transformed from the paleo changjiang river to the paleo huanghe river yellow river near the late mis 3 implying that the paleo huanghe river likely emptied into the sys and built a large delta during the mis 3 interval a strong summer monsoon during the early mis 1 interval was favorable for the changjiang to deliver abundant sediments to the study core area a weak summer monsoon during the mid late mis 1 when the coastline had retreated to nearly its present day position decreased the changjiang and huanghe supply to the study area low sediment supply and sufficient accommodation space gave rise to the development of sediment starved systems during this period nd values fluctuated between the changjiang and huanghe sources at that time suggesting that sea bed erosion materials are the main sediment contribution to the study area in general sedimentary evolution in the western sys since mis 3 is a good example of river sea interaction in the marginal seas of southeast asia in which sea level and monsoonal climate changes should play an important role

transgressive and highstand systems tracts and post glacial transgression the east china sea abstract the late pleistocene holocene depositional sequence on the shelf in the east china sea ecs is interpreted on the basis of the analyses of four sediment cores and high resolution seismic reflection sub bottom profiler records along a ne sw across shelf transect sedimentary strata deposited above a lowermost planar erosional surface that was formed during sea level fall of the last glacial are divided into two units along a ne sw across shelf transect changjiang okinawa the lower unit is characterized by seaward dipping tangential clinoforms with a thickness of 30 40 m at mid shelf depths and less than 30 m beneath the outer shelf prograding clinoforms are more obvious in mid shelf environments the upper unit is characterized by an upper transparent layer that is formed into ridge and swale topography the boundary between the upper and lower units is sharp and erosional surficial sediments taken by cores from the central ecs shelf are also divided into two facies a sandy facies consisting of sand or sandy gravel with moderately abundant molluscan shell fragments and a muddy facies comprising mud intercalated with thin sand layers the sandy facies is widely distributed on the middle to outer shelf seafloor and has a measured thickness of 30 cm up to several metres radiocarbon ages of molluscan shells in this sediment are less than approximately 10 ka bp except for ages from basal shell lag deposits which are 10 40 ka bp the muddy facies underlies the sandy facies and has radiocarbon ages of 2 7 2 9 ka bp previous work and 20 38 ka bp this study and tl ages of 27 50 ka bp previous work the boundary between these lithologic units is an erosional sharp contact the sandy and muddy facies are correlated with the upper and lower seismic units respectively the lower unit is characterized by prograding clinoforms and is interpreted to represent deltaic or nearshore tidal ridge sediments of the paleo changjiang river that were deposited during the last glacial lowstand of sea level as a lowstand systems tract the underlying erosional surface is interpreted to be a sequence boundary formed as a regressive marine erosional surface during the fall of sea level the erosional boundary between the lower and upper units is interpreted as a transgressive surface of erosion formed during the subsequent rise of sea level the upper unit has a modern sand ridge topography and is interpreted to represent offshore shelf sand ridges of the transgressive to highstand systems tract

the castlegate sandstone of the book cliffs utah sequence stratigraphy paleogeography and tectonic controls abstract earlier stratigraphic work had predicted that at the type section of the castlegate formation the castle gate near price utah the unit consists of two sequences separated by a sequence boundary representing approximately one million years of unrecorded time although the type section is well exposed it consists of a monotonous succession of braided fluvial sandstones and no obvious boundary can be identified using facies criteria this is a good example of a cryptic sequence boundary petrographic data indicate however a significant change in detrital composition 20 m above the base of the section at a through going erosion surface that is therefore interpreted as the sequence boundary revised sequence correlations together with other petrographic data and regional paleocurrent patterns provide the basis for a model of the paleogeographic evolution of the area rocks assigned to the castlegate sandstone comprise two or possibly three sequences formed at times of slow regional subsidence erosional sequence boundaries and tilts in paleoslope between each sequence record thrust loading and unloading of the basin and the growing influence of intrabasinal upwarps movement of which was beginning to be affected by laramide movements toward the end of castlegate sedimentation

major sinks of the changjiang yangtze river derived sediments in the east china sea during the late quaternary the east china sea ecs is a typical marginal sea located between the eurasian con tinentandwestpacificocean inthisstudy wereviewstate of the artresearchprogressonthepos sible sinks of the changjiang derived sediments in the ecs during the late quaternary the major sinks of these sediments in the ecs are on the outer shelf and the okinawa trough during the last glacial maximum corresponding to a lowstand of sea level during the deglacial marine transgres sion the gently dipping shelf was rapidly inundated and strong tides prevented fine sediment from deposition on the open shelf resulting in the development of a unique tidal sand ridge sys tem with sea level reaching the present situation and the modern marine environment being com pleted in the early holocene the changjiang sediments mostly accumulated in the river s estuary to build a large delta with only a fraction reaching the inner shelf and coastal embayments the late quaternary changes in monsoon climate induced river flux sea level and oceanic circulation primarily controlled the source to sink transport of the changjiang sediments in the ecs and fur ther determined the stratigraphic framework and sedimentary facies on the shelf

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

clastic sequences developed during late quaternary glacio eustatic sea level fluctuations on a passive margin example from the inner continental shelf near barnegat inlet new jersey analysis of 100 km of seismic reflection geopulse profiles from a 47 km 2 grid on the new jersey low mesotidal inner continental shelf near barnegat inlet reveals that the upper 30 m is composed of 3 unconformity bounded units vibracores 1 6 m long recovered from 12 sites contain several lithofacies reflecting a variety of depositional environments that existed during late quaternary glacioeustatic sea level fluctuations on this slowly subsiding passive margin with low sediment supply environments include rivers during glacial and stadial lowstands of the sea and a barrier island lagoon complex as well as pro barrier ebb tidal delta shore attached and detached ridges and below storm wave base shelf during interglacial or inter stadial highstands following the last major interglacial 125 ka sea level fell and rivers eroded a planar seaward dipping surface r1 by early wisconsinan time 70 ka as sea level rose during the mid wisconsinan 55 ka a barrier island system migrated to within 0 2 1 7 km of the modern barrier shoreline leaving a 4 to 6 m thick record depositional sequence i maximum highstand of the mid wisconsinan sea level was 20 m below present sea level fell again during the late wisconsinan 20 ka and rivers again flowed across the exposed shelf creating an unconformity r2 a barrier lagoonal system developed under rising sea level by at least early middle holocene time based on peats 8810 170 yr b p cored from 12 m the mid wisconsinan 55 ka barrier system was preserved under these early holocene transgressive sediments lower unit of depositional sequence ii lower transgressive tract the modern barrier and inner continental shelf deposits upper unit of depositional sequence ii upper transgressive tract are relatively thin average 3 4 m pebbly sands overlying a prominent unconformity a transgressive surface r3 formed by marine erosion during the holocene sea level rise both the ebb tidal delta and shore attached linear sand ridges act as partial shields to wave and tidal current erosion of the muddy sub strate below r3 in the nearshore area this shielding is creating a transgressive surface marine unconformity of relatively high relief 3 7 m

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

alluvial evidence for major climate and flow regime changes during the middle and late quaternary in eastern central australia as a low gradient arid region spanning the tropics to the temperate zone the lake eyre basin has undergone gentle late cenozoic crustal warping leading to substantial alluvial deposition thereby forming repositories of evidence for palaeoclimatic and palaeohydrological changes from the late tertiary to the holocene auger holes and bank exposures at five locations along the lower 500 km of cooper creek a major contributor to lake eyre in the eastern part of the basin yielded 85 luminescence dates tl and osl that combined wit a further 142 luminescence dates from northeastern australia have established a chronology of multiple episodes of enhanced flow regime from about 750 ka to the holocene mean bankfull discharges on cooper creek upstream of the innamincka dome at 250 230 ka or oxygen isotope stages ois 7 6 are estimated to have been 5 to 7 times larger than those of today however substantially less reworking has occurred during and after ois 5 than before lower cooper creek appears to have similarly declined in the tirari desert adjacent to lake eyre there is evidence of widespread alluvial activity perhaps during but certainly before the middle pleistocene yet the river became laterally restricted in ois 7 to 5 while the quaternary has been characterised by a dramatically oscillating wet dry climate since oxygen isotope stage ois 7 or 6 there has been a general decline in the magnitude of the episodes of wetness to which the eastern part of central australia has periodically returned during the last full glacial cycle cooper creek s periods of greatest runoff and sand transport were not during the last interglacial maximum of ois 5e 132 122 ka but later in ois 5 when sea levels and global temperatures were substantially below those of 5e or today fluvial activity returned in ois 4 and 3 but not to the extent of mid and late ois 5 strongly seasonal but still powerful flows transported sand and fed source bordering dunes in ois 5 and 3 this chronology of fluvial activity in the late quaternary broadly coincides with that for rivers of southeastern australia and suggests that the wet phases in eastern central australia have not been governed as much by the northern monsoon as by conditions in the western pacific close to the east coast both north and south flow confinement within the innamincka dome has locally amplified cooper creek s energy and here evidence exists for short but high magnitude episodes of flow during the last glacial maximum and in the early to middle holocene conditions that were capable of forming large palaeochannels but that were not long lived enough to rework the river s extensive floodplains elsewhere along its length

variations in temperature and salinity of the surface water above the middle okinawa trough during the past 37 kyr abstract east china sea ecs is an important climate modulator of east asia in the last glacial period the global sea level the path and strength of the kuroshio current experienced great changes combined with the variable volume of fresh run off input they made the hydrographic situation in the ecs quite different from nowadays based on high resolution alkenone sea surface temperature sst and oxygen isotope composition of planktonic foraminifera globigerinoides sacculifer we reconstructed paleo sea surface salinity sss of a long piston core dgks9604 retrieved from the middle okinawa trough of the eastern ecs the 18o and sst records display significant variations with global ice volume synchrony of the millennial scale climate events like yd and heinrich events of core dgks9604 to the ice core from the northern high latitudes and the synchroneity of deglacial warming with the bolling allerod warming suggests a strong coupling of the sst variations in the marginal pacific ocean to the climate of the north atlantic most likely through the asian monsoon atmospheric circulation the ecs documents lowest sst 22 c at 26 cal kyr bp and 3 c sst difference between the full glaciation 26 to 19 cal kyr bp and mid to late holocene 6 cal kyr bp present the overall long term hydrographic variations in the middle okinawa trough are controlled by temporal and spatial variations in i the intensity and position of the kuroshio current ii intensity of the asian summer monsoon and iii sea level fluctuations coupled with ecs topography saline surface water dominated over the middle okinawa trough during early pre glaciation 37 to 31 cal kyr bp last deglaciation 19 to 11 6 cal kyr bp and mid to late holocene 6 cal kyr bp present whilst freshened surface water prevailed during the late pre glaciation 31 to 26 cal kyr bp full glaciation 26 to 19 cal kyr bp and early holocene 11 6 to 6 cal kyr bp

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

delta development and channel incision during marine isotope stages 3 and 2 in the western south yellow sea abstract approximately 4100 km of high resolution seismic profiles recently obtained from the western south yellow sea were subdivided into seven seismic units by six major seismic surfaces three sediment cores between 60 and 71 m in length obtained from localities on the seismic profile lines were analyzed for sedimentary characteristics clay mineral components and benthic foraminiferal and ostracod assemblages and were also dated by ams 14 c and optically stimulated luminescence to document the environmental history of the region stratigraphic units in the cores were confidently correlated with seismic units in the profiles stratigraphic correlation among these three cores and the previous well studied core qc 2 was facilitated by the cold water deposits in marine isotope stage mis 5 the three cores document the sedimentary sequence during the period from mis 6 up to mis 1 strata formation and sedimentary environment changes since mis 5 are strongly controlled by sea level fluctuations most of the successions were formed in mis 5 mis 3 and mis 1 with major erosions in mis 4 and mis 2 particularly our data revealed the presence of a large delta active during mis 3 likely from the early stage of mis 3 to about 40 cal kyr bp that was subsequently affected by channel incision the delta succession and incised channel fills have a high concentration of smectite in their clay mineral components suggesting that the paleo yellow river was the main contributor to the delta development and channel incision the delta sequence has a coarsening upward trend and consists of two seismic facies the upper facies shows lateral alternations of chaotic and oblique or very low angle reflectors which correspond to sandy proximal delta front and delta plain facies and the lower facies is characterized by seaward dipping clinoforms which correspond to muddy distal delta front and prodelta facies the top surface of the delta inclines very gently seaward consistent with a deltaic development associated with the sea level fall in mis 3 the incised channel system consists of two main channels with multiple tributaries in a dendritic pattern the incised channel fills begin with fluvial and then estuarine sediments which are truncated by a transgressive ravinement surface and capped by transgressive deposits the main incision channels have a terraced cross sectional morphology which is interpreted to reflect multiple episodes of sea level fall during incision presumably from the late mis 3 to the last glacial maximum

coalescent valley fills from the late quaternary record of tuscany italy abstract three prominent incised valley fills of post last glacial maximum age are described from the northern tuscan coast of italy stratigraphic correlation of core data along a cross section transversal to the present fluvial channel axes enables identification of a suite of genetically related valley bodies that fill the incisions made up by arno serchio and camaiore stiava rivers during the last glacial interglacial cycle the valley fills display different shapes and size but remarkably similar facies architecture valley bodies range between 5 and 10 km in width and between 30 and 45 m in thickness with width thickness ratios of about 100 300 above a lowstand and early transgressive gravel fluvial deposit the three incised valley fills display a distinctive succession of coastal plain to estuarine facies dated to about 13 8 cal ka bp radiocarbon dates document that the three valleys were active simultaneously accommodation space was rapidly created during transgression and then filled under conditions of very high sediment accumulation about 1 cm y in contrast to the more common deepening upward trend recorded by the latest pleistocene early holocene valley fill successions worldwide sedimentation in the tuscan valleys equalled or even exceeded the rate at which accommodation was created thus leading to an aggradational rather than backstepping stacking pattern of high frequency millennial scale parasequences above the valley fills and on the interfluves a thin deepening upward succession of nearshore deposits marks the rapid change from aggradational to retrogradational depositional style this is invariably overlain by a characteristic shallowing upward motif of prograding deltaic and coastal facies the maximum flooding surface which can be tracked across the whole study area on the basis of subtle palaeontologic indicators is shown to represent an almost isochronous surface dated to about 7 8 cal ka bp through examination of large scale geometry and facies attributes of the valley fills including the relationships between valley bodies and interfluves this study represents an example of how adjacent river systems with significantly different characteristics may respond simultaneously in a consistent manner to rapid changes in sea level and climate conditions

lower miocene gypsum palaeokarst in the madrid basin central spain dissolution diagenesis morphological relics and karst end products the miocene sedimentary record of the madrid basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations one of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units the miocene lower and intermediate units of the madrid basin the palaeokarst formed in lacustrine gypsum deposits of aragonian age and corresponds to a surface palaeokarst epikarst further buried by terrigenous deposits of the overlying unit karst features are recognized up to 5ae5 m beneath the gypsum surface exokarst and endokarst zones are distinguished by the spatial distribution of solution features i e karren dolines pits conduits and caves and collapse breccias sedimentary fills and alteration of the original gypsum across the karst profiles the development of the gypsum palaeokarst began after drying out of a saline lake basin as supported by recognition of root tubes later converted to cylindrical and funnel shaped pits at the top of the karstic profiles the existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution and explains the limited depth reached by both exokarst and endokarst features synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi arid climates duration of karstification is of the order of several thousands of years which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time

lake evolution during the past 30 000 years in china and its implications for environmental change abstract taking china as a whole lake expansion occurred 500 b c 0 a d 650 950 a d and 1250 1650 a d over the past 3000 yr the expansions were mainly due to climatic fluctuations and correspond to frequent flood reports three regional characteristics of lake development have been recognized 1 fluctuations of near coastal lakes and those in other regions as well were out of phase during 500 b c 500 a d which possibly resulted from out of phase fluctuations of climate and sea level on 10 to 100 yr time scale 2 as the lower yellow river channel migrated southward the lakes in the south of the north china plain formed and reached their largest sizes much later than those in the north 3 for the lakes in the middle and lower yangtze river valley the higher a lake basin lies above a neighboring river and the further the lake is from the river s mouth in general the younger the lake is through land reclamation the ancient chinese have changed most of the lakes greatly however human activities were also constrained in certain ways by the natural changes of the lakes reclamation usually was banned and farmland was abandoned to repair reservoirs while lakes were expanding

development of depositional systems in the southeastern yellow sea during the postglacial transgression this study focuses on the development of depositional systems in the southeastern yellow sea during the postglacial transgression based on the analysis of closely spaced high resolution seismic profiles chirp and piston cores transgressive deposits comprise the paralic component of estuarine channel fills seaward prograding wedge and along shore prograding mound and the marine component of sand veneer mud blanket and offshore ridge these transgressive deposits were developed through three distinctive stages in terms of possible sea level position during the early stage tidal sand ridges and sand veneer formed south of jeju island resulting from shoreface erosion associated with a relatively slow transgression the following transgression in the middle stage inundated subaerially formed interfluves along the central part of the sea and affected development of estuarine environments with increasing tidal regime in the eastern part of the sea combined with the strong tidal reworking insufficient sand supply enhanced the formation of erosional ridges short period increase in fluvial discharge affected the deposition of coastal wedge in the western part fine grained sediments from either fluvial discharge or tidal reworking were dispersed seaward to form mud blanket the late stage was characterized by the deposition of veneered sands off the jiangsu coast which was due to relatively slow rise in sea level further offshore along shore prograding mound was constructed by huanghe derived sediment influx and subsequently eroded and redeposited by wave and tide activities thus detached from the proximal source the depositional processes and variability of the transgressive deposits in the southeastern yellow sea were largely controlled by changes in rate of sea level rise during the transgression most likely related to the global flooding events triggered by melt water pulses the changes in shoreline configuration and oceanographic regime have also influenced the distribution and morphology of the transgressive deposits a short period increase in riverine discharge caused the temporal sediment progradation off the jiangsu coast

sequence stratigraphy seismic profiles and cores of pleistocene deposits on the rhone continental shelf abstract high resolution seismic profiles on the rhone deltaic shelf has shown the existence of a complex of pleistocene superimposed prograding wedges interrupted by a major incised valley system cutting across the shelf the individual wedges are interpreted from internal geometry and coring data as prograding shoreface deposits accumulated during periods of relative sea level lowering punctuated by small scale relative sea level falls or forced regressions they are related to 5th order glacio eustatic cycles and are stacked to form a composite 4th order sequence radiocarbon dating tandetron ams of the upper wedge to 40 ka bp indicates a stratigraphic hiatus across the shelf corresponding to the glacial maximum lowstand at the end of the wurmian cycle isotopic stage 2 during which sea level had dropped to 120 m below present sea level seaward tilting of the wedge boundaries indicate that the shelf has been subjected to differential subsidence that provides the necessary accommodation space for deposits to accumulate on the mid outer shelf the seaward tilting results from a cumulative effect of sediment and hydrostatic loading tectonism is also expressed by a westward shore parallel tilting in the area east of the incised valleys the amount of tilting the stacking pattern of the wedges and the location of incised valleys are structurally controlled by the alpine orogen which dips westward under the rhone margin the tectonic component interacts with glacio eustatic sea level fluctuations and accounts for the partition of the shelf into two areas with specific features separated by the rhone incised valleys

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

the sedimentary record of palaeoenvironments and sea level change in the gulf of carpentaria australia through the last glacial cycle abstract environmental evolution of the gulf of carpentaria region the world s largest tropical epicontinental seaway through the last glacial cycle has been determined from a series of six sediment cores these cores form the focus of a multi disciplinary study to elucidate sea level climate and environmental change in the region the sedimentary record reveals a series of facies including open shallow marine marginal marine estuarine lacustrine and subaerial exposure throughout the extent of the basin during this period the partial or complete closure of the central basin from marine waters results from sea level falling below the height of one or both of the sills that border the gulf the arafura sill to the west 53 m below present sea level bpsl and torres strait to the east 12 m bpsl the extent and timing of these closures and restriction of the shallow waterbody within are intrinsic to local ocean circulation available latent heat transport and the movement of people and animals between australia and new guinea whilst the occurrence of the palaeo lake carpentaria has previously been identified this study expands on the hydrological conditions of the lacustrine phases and extends the record through the last interglacial detailing the previous sea level highstand mis 5 5 and subsequent retreat when sea levels were low during the mis 6 glacial period the gulf was largely subaerially exposed and traversed by meandering rivers the mis 5 transgression 130 ka bp led to marine then alternating marine estuarine conditions through to mis 4 70 ka bp when a protracted lacustrine phase of varying salinity and depth area and including periods of near desiccation persisted until about 12 2 cal ka bp the lake expanded to near maximum size 190 000 km 2 following the intensification restoration of the australian monsoon at 14 ka bp this lake full phase was short lived as by 12 2 cal ka bp marine waters were entering the basin coincident with the progressive sea level rise fully marine conditions were restored by about 10 5 cal ka bp by westward connection to the arafura sea indian ocean whereas connections to the pacific ocean coral sea did not occur until about 8 cal ka bp

tributary distributary and other fluvial patterns what really represents the norm in the continental rock record abstract this paper evaluates the recent claim made by weissmann et al 2010 that deposits of distributive fluvial systems dfs may form the bulk of the continental fluvial record weissmann et al 2010 define dfs as a pattern of channel and floodplain deposits that radiate outward from an apex that is located where the river enters the sedimentary basin as such dfs are fan like systems on which multiple channels coexist and distribute water and sediment across the fan published criteria for the recognition of dfs weissmann et al 2010 are 1 a radial pattern of channels from the dfs apex 2 downslope decreases in channel size 3 down dfs grain size decreases and 4 a lack of lateral channel confinement however in weissmann et al 2010 and subsequent papers only the first of these criteria is applied rigorously thus allowing a variety of types of fluvial system including avulsive incised anabranching and coastal plain distributary systems to potentially be classified uncritically as dfs an ancient succession formed by dfs should preserve mostly small channel bodies with a limited range of dimensions and no outsized channel bodies channel bodies in dfs dominated successions should also decrease in size in a down palaeoslope direction and show palaeocurrent relationships indicative of radial dispersal in order for the term dfs to be applied these characteristics should also be established within stratigraphic bodies that formed coevally however very few examples have yet been published that satisfy these criteria if the claim that dfs dominate the alluvial stratigraphic record is valid then few if any sedimentary bodies formed by large channels should be preserved a review of published research demonstrates however that the alluvial stratigraphic record contains a broad diversity of fluvial network styles including abundant representatives of tributary avulsive anabranching and incised in addition to distributary types it is also clear that the deposits of large main stem rivers that are comparable to the big rivers of the modern world are abundantly preserved in the stratigraphic record an analysis of the planimetric area of modern tributary and distributary fluvial systems is presented demonstrating that tributary systems are also likely to represent a far larger proportion of the ancient sedimentary record than dfs the body of evidence presented herein from modern and ancient alluvial systems thus suggests that the hypothesis of weissmann et al 2010 should be wholly rejected dfs do not dominate the continental stratigraphic record

upstream controls on incised valley dimensions and fill examples from the upper mississippian mauch chunk group central appalachian basin usa abstract subsurface mapping and facies and architectural element analysis on outcrop combined with published detrital zircon geochronology and sandstone petrography are used to reconstruct a source to sink system for two incised valley fills in the upper mississippian mauch chunk group the lower stony gap incised valley is relatively broad and filled with quartzarenite fluvial facies consisting of downstream accreting elements with minimum thicknesses of 6 m cross sets within elements average 62 5 cm thick the lower princeton incised valley is relatively narrow and filled with sublitharenite fluvial facies consisting of channel elements that range in thickness from 0 25 to 3 6 m cross sets within elements average 35 cm thick quantitative estimates of drainage areas using regional hydraulic geometry curves for comparable climatic settings are consistent with order of magnitude differences for the lower stony gap sandstone 700 000 km2 and the lower princeton formation

late pleistocene dune chronology near coastal new south wales and eastern australia abstract late pleistocene aeolian activity is manifested stratigraphically and geomorphically along the new south wales coastline in six different ways as barrier dunes cliff top and headland dunes sand sheets on slopes reworked barrier features onlapping coastal sand bodies and dustings the majority of activity took place over the last 40 ka bp paradoxically the present interglacial is characterised by extensive coastal dune fields while the last interglacial is not a fact that cannot be solely attributed to the destruction of older deposits through time the similarity in the degree of dune building between the holocene and the last glacial under very different climatic regimes may be indicative of the interaction of a multitude of climatic factors the effects of aboriginal occupation and burning also cannot be excluded australia wide aeolian activity has preferentially lingered over the northeastern and southern parts of the continent during the last glacial in the north this lingering reflects the progressive drying out of northern australia with the demise of trade wind cyclone and monsoon activities in the southeast it reflects the enhancement of stable extensive high pressure cells leading to the displacement of cold fronts and strong winds either southward towards tasmania or offshore into the tasman sea

late quaternary sedimentation and high resolution sequence stratigraphy of the east texas shelf the shelf margin deltas of the area show a complex pattern of progradation and aggradation that varies from one delta to the next this complexity is due predominantly to the different response of systems with different sediment supplies to fifth order eustatic fluctuations before we understood these autocyclic effects attempts at relating seismic stratigraphic changes to the oxygen isotope curve our proxy for sea level change were unsuccessful

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

aeolian fluvial interaction and climate change source bordering dune development over the past 100 ka on cooper creek central australia abstract this study provides an interpretation of interrelated quaternary fluvial and aeolian activity related to climate change on cooper creek in the lake eyre basin in southwestern queensland central australia the extensive muddy floodplain is characterised by buried sandy palaeochannels now almost entirely invisible but stratigraphically connected to source bordering dunes that emerge as distinctive sandy islands through the floodplain surface luminescence dating has identified pronounced periods of fluvial activity represented by abundant sandy alluvium from marine isotope stages mis 8 3 while all these sandy fluvial episodes on cooper creek were much more powerful than anything subsequent they appear to be ranked in order of declining activity mis 8 6 saw reworking of almost the entire floodplain whereas subsequent phases of reworking were far less extensive source bordering dunes were derived from active sandy channels in late mis 5 85 80 ka and mid mis 3 50 40 ka after 40 ka sand channel activity largely ceased and the floodplains and channels were inundated with mud isolating the dunes as emergent features although aeolian reworking of the upper parts of some dunes has continued to the present they show remarkable resilience having survived without appreciable migration for at least 40 ka whilst the channels once determined the location of source bordering dunes in an interesting role reversal the remnant dunes now determine the position of many contemporary flood channels and waterholes by deflection and confinement of overbank flows

control of upstream variables on incised valley dimension abstract it is well documented that sea level fell during the last glacial maximum shifting graded stream profiles out of equilibrium and causing rivers to incise into continental shelves although incised valleys have been heavily researched the interplay between upstream and downstream controls on incised valley dimension are not well constrained to address this lack of understanding we examined the cross sectional dimension of nine incised valleys located across the northern gulf of mexico margin and bounded by the sequence boundary associated with the last sea level lowstand these incised valleys are distinguished by drainage basins that vary in size by three orders of magnitude cover a margin that presently has a steep climate gradient and extend across a continental shelf that varies along strike in width and gradient incision depths vary for valleys that have similar gradient profiles but different drainage basin areas suggesting significant control of upstream variables on incised valley morphology additionally these data show a strong linear correlation between drainage basin area and incised valley cross sectional area this suggests applicability of the empirically derived relationship between modern discharge and cross sectional channel area to incised valleys when compared at the maximum highstand shoreline of the previous sequence incised valley dimension adjusts over a longer period than the lowstand and is in equilibrium with drainage basin area which is considered a proxy for long term discharge although base level fall promotes incision upstream variables control incised valley dimensions

the nature and significance of variations in gypsum crystal morphology in dry lake basins depressions in semiarid regions with a gypsiferous geological substrate commonly contain highly gypsiferous sediments with gypsum that formed either as a synsedimentary precipitate during perennial or ephemeral lake stages or as a diagenetic precipitate during saline mudflat stages the dry to ephemeral lake basins of the monegros region in northern spain are depressions of this type and provide a unique opportunity to examine whether and how conditions of gypsum formation are reflected by gypsum crystal morphology yielding information that can contribute to a correct interpretation of the depositional environment of gypsum in ancient and modern formations in most lake basins of the study area the sediment fill consists of a similar sequence of three lithological units the lower unit includes fragmented gypsum crystals in some basins recording clastic reworking and in other depressions it contains large lenticular crystals formed as phreatic diagenetic precipitates the middle unit typically contains synsedimentary gypsum with a non lenticular morphology modified by postdepositional processes but it also comprises synsedimentary lenticular gypsum in some basins in the upper unit separated from the underlying interval by a marked hiatus both synsedimentary and diagenetic gypsum are present the former including layered gypsum deposits with features such as grading and variations in crystal morphology the results show that a non lenticular crystal habit of gypsum occurring within the groundmass sediment matrix indicates synsedimentary precipitation in contrast a lenticular crystal habit cannot be used in isolation as an indicator of the environment in which the gypsum initially precipitated unambiguously late diagenetic gypsum includes fine grained precipitates in voids created by soil fauna these infillings consist of initially non lenticular crystals with a tabular prismatic habit recording that conditions promoting lenticular crystal growth do not always prevail outside the groundmass in soil related settings and illustrating the importance of knowing the context of analyzed gypsum occurrences at the scale of a sample

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

late quaternary lacustrine groundwater aeolian and pedogenic gypsum in the prungle lakes southeastern australia abstract detailed petrographic studies of recent or sub recent evaporites where many critical environmental parameters are defined can help in the analysis of ancient deposits and in the establishment of chemical and environmental models for evaporite formation the prungle lakes are part of the now dry willandra lakes system in semi arid southwestern new south wales the willandra lakes have been a site of cyclic quaternary sedimentation in response to the well documented global climatic fluctuations associated with the glacial interglacial cycle at times of hydrologic stress low lake levels are associated with high salt volumes inherited from evaporative concentration in large shallow lakes upstream and the inflow of saline groundwaters thus at prungle a complex array of concentric shorelines lake floor terraces and lunettes has developed as basin within basin landforms which formed in response to filling and drying cycles sediments associated with these geomorphic units include 1 1 freshwater littoral nearshore and deep water deposited laminated sands and muds with biogenic carbonates chiefly of ostracodal and algal origin 2 2 evaporites comprising interbedded clay and laminated gypsum clay couplets which consist of discrete thin laminae of sugary white euhedral prismatic gypsum separated by detrital clay layers with a high degree of optical orientation primary accessory celestite srso4 occurs as discrete patches within the gypsum laminae 3 3 groundwater pyramidal discoidal or lenticular gypsum crystals grown from supersaturation produced by evaporation at the capillary fringe of the water table these have formed displacively within the sediments and caused considerable disruption of the sediment matrix 4 4 aeolian deposition in irregular transverse ridges of sand sized reworked groundwater gypsum and disrupted lacustrine clays the gypsum crystals are predominantly discoidal pyramidal forms which are conspicuously oriented parallel to bedding well sorted and extensively corroded the clay pellets are well sorted and moderately well rounded higher in the profile bedding is indistinct due to pedogenic processes which include modification of detrital grains and secondary crystallization of gypsum and carbonate a thin gypcrete horizon occurs at the surface the last cycle of sedimentation in the prungle lakes is believed from correlation with lakes higher in the willandra system to have occurred during the period 50 000 16 000 yr b p since then groundwaters have dropped below the zone of interaction with the lake floor and surface water no longer reaches the lakes sedimentation has ceased and soil formation with secondary carbonate and gypsum has continued to the present a range of sedimentary environments is identified which depend on strong seasonal oscillations these environments are virtually absent from the australian continent today and their occurrence during the pleistocene supports the contention of enhanced climatic seasonality at that time the array of sediment types and mineralogies is almost identical to that characteristic of coastal sabkha sequences highlighting the difficulty of relying on unusual evaporative mineralogy to differentiate marine and non marine environments detailed petrographic analyses of the prungle sequence have been made in association with a review of theoretical experimental and observational studies of the environmental controls of calcium sulfate mineralogy and crystal habit this has enabled the correlation at prungle of depositional environment with gypsum petrofacies and associated compositional fabric or structural features these observations are more generally applicable to other evaporite deposits many gypsum evaporites reported in the literature have been compared with this scheme developed at prungle

organic geochemistry of the lower cretaceous black shales and oil seep in the sinop basin northern turkey an oil source rock correlation study abstract in the sinop basin a thick liassic to quaternary sedimentary section is exposed a lower cretaceous aged caglayan formation crops out in the basin and consists of claystone siltstone sandstone marl and black coloured shale that exhibits a fair to good source rock potential an oil seep from the caglayan formation is located in the ekinveren region of the sinop basin the average total organic carbon toc values of two shale samples from the caglayan formation in the ekinveren and the burnuk sections ekin 8 bur 7 are 1 48 and 1 26 wt respectively and the hydrogen index hi values are 190 and 244 mghc g toc respectively the potential yield py value of the samples is 2 0 mghc g rock which indicates fair good hydrocarbon potential for the caglayan formation a unimodal n alkane distribution with dominant light end components is observed on the gas chromatograms of the shale samples from the caglayan formation low tar terrigenous aquatic organic matter ratios low c 19 c 20 c 23 tricyclic terpane ratios and a higher type ii kerogen content indicate that the shale samples predominantly contain marine organic matter the pr ph ratios of the shale samples are 1 39 and 0 89 respectively the pr ph values in combination with a high c 30 diahopane c 29 ts ratio imply a suboxic anoxic depositional environment for the caglayan formation the t max values of the ekinveren and burnuk shale samples are in the range of 425 432 c and 431 434 c respectively and the average t max values are 429 c and 433 c respectively based on the t max data the caglayan formation shales are immature early mature in the ekinveren location and early mature mature in the burnuk location the cpi values isoprenoid n alkane ratio 20s 20s 20r c 29 sterane and 22s 22s 22r c 32 homohopane ratios indicate that the shales from the burnuk location are more mature than those of the ekinveren location the large ucm unresolved complex mixture and low amounts of n alkanes and isoprenoid alkanes observed in the gas chromatogram of the oil seep indicate that the oil has been heavily biodegraded the m z 191 and m z 127 mass chromatograms of the samples from the caglayan formation and the ekinveren oil seep were similar in their distributions of tricyclic terpane c 23 dominant c 24 tetracyclic terpane norhopane hopane homohopane with dominant c 31 and a decreasing amount of the higher number homologues diasterane and pregnane the c 27 c 28 and c 29 sterane distributions for the oil and the shale samples were also similar demonstrating a c 27 c 29 c 28 relationship thus the biomarker data strongly indicate that the black shales and the ekinveren oil seep are related to each other in other words the oil has been derived from the caglayan formation

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

lake eyre palaeohydrology from 60 ka to the present beach ridges and glacial maximum aridity lake eyre is presently an ephemeral playa lake in an extremely large 1 3 million km2 internal drainage basin with most of its inflow derived from monsoon watered northern australia the hydrologic state of the lake has varied in the past in response to climate change from a perennial lake up to 25 metres deep to a groundwater controlled playa marked by substantial sediment deflation this paper is concerned with the stratigraphic record of the last 60 ka of that hydrologic history particularly the character and age of a playa marginal unit formed by deflation from the playa and of stranded high beach ridges a major deflation episode between 60 and 50 ka excavated the present lake eyre basin and deposited a gypsum and clay rich aeolian phase the williams point aeolian unit at a number of sites around the lake after deflation ceased a thick secondary gypsum profile developed on the dune early in oxygen isotope stage 3 evidence for the state of lake eyre at this time is equivocal preliminary results from a substantial suite of amino acid racemization aar analyses of mollusc shell and bird eggshell samples from beach ridges at 5 and 10 m australian height datum ahd suggest that they are oxygen isotope stage 5 in age sedimentologic evidence suggests that it is unlikely that the shells are reworked from older deposits these aar results apparently conflict with early oxygen isotope stage 3 thermoluminescence tl dates from the 5 m ahd beach ridge nanson et al this volume however the age difference is not substantial the calibration of the aar is still at a preliminary stage and only one site was sampled for both techniques further stratigraphic and chronologic work is required to fully assess the apparent discrepancy between about 30 000 and 12 000 yr b p lake eyre was at least as dry as it is today at many sites around madigan gulf a lunette like playa marginal aeolian unit the shelly island unit was deposited during this period formed by material deflated from the playa floor forty ams radiocarbon dates span the period 35 000 to 10 000 yr b p from the shelly island unit 11 and from aeolian sediment close to playa level 29 indicating that the lake was dry during this period this evidence conflicts strongly with 2 tl dates from latest oxygen isotope stage 3 and oxygen isotope stage 2 from the 5 and 10 m ahd beach ridges nanson et al this volume additionally the aar results from the high beach ridges cannot be reconciled with these tl dates after 10 000 yr b p a minor lacustral phase occurred until the modern ephemeral playa regime became established at 3000 4000 yr b p

the role of playas in pedogenic gypsum crust formation in the central namib desert a theoretical model the formation of namibia s extensive pedogenic gypsum crusts caso4 2h2o is interpreted in a new light it is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration such as inland playas and that deflation of evaporitic rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricrusts on the coastal gravel plains of the namib desert surrounding these playas this study establishes the nature extent and distribution of playas in the central namib desert and provides evidence for playa gypsum deflation and gravel plain deposition remote sensing shows the distribution of playas captures ongoing deflation and provides evidence of gypsum deflation it is proposed that following primary marine aerosol deposition both inland playas and coastal sabkhas generate gypsum which through the process of playa deflation and gravel plain redeposition contributes to the extensive pedogenic crusts found in the namib desert region copyright 2001 john wiley sons ltd

late pleistocene evolution of salt lakes in the qaidam basin qinghai province china abstract the qaidam basin is a tectonically controlled depression at 2700 m altitude on the northern margin of the qinghai xizang tibet plateau rimmed by the high aljun qilian ranges to the north and kunlun peaks to the south rising above 5000 m the basin floor experiences hyper arid conditions with evaporation precipitation ratios exceeding 100 1 periglacial and glacial conditions prevail on montane peaks with permafrost above 3800 m on the basin floor small waterbodies lie on extensive halite salt flats on the largest the qarhan salt flat 5800 km2 in extent the small lakes dabuxun and taijinier represent contracted remnants of a once expansive water body throughout neogene time a succession of clastic sediments indicates lake depo centre migration from nw to se towards late pliocene evaporitic conditions developed with formation of gypsum halite celestite mirabilite and bloedite continued deformation through pleistocene time has developed a series of nw se trending domes and troughs this setting has continued to exert a controlling influence on basin and brine evolution with progressive development through sulfate to chloride brines as dry conditions intensified in late pleistocene expanded lake conditions qarhan mega lake corresponding to near the 2800 m contour indicate the existence of past climates much more humid than those of today a drilling program has defined the lateral and vertical extent of evaporitic halite deposits freshwater clastics and shell deposits which predate the halite phase indicate humid lacustral conditions until after 40 000 30 000 yr b p desiccation from about 25 000 yr until about 9000 yr b p resulted in deposition of halite to 60 m thick with thin parting muds representing brief returns to more humid environments high lake shorelines with aragonitic ooids surrounding the dry playa kunteyi and high level ostracod rich beach and near shore deposits on xiao qaidam attest to the presence of expanded late pleistocene lacustral conditions on lakes other than qarhan preceding the final evaporite stage clastic sediments associated with the halite are dominated by loessial silts equivalent to the late pleistocene malan deposits of central china simultaneous halite and loess deposition reflect the dry conditions that developed in the qaidam basin during the latter part of the last glaciation and which have persisted ever since the final evolution of brines has resulted in development of extensive potassium rich brines and salts with the mineral carnallite providing the basis for a large potash extraction industry near golmud the hydrologic history documented by the analyses of lake sediments reflects the interaction of tectonic deformation and climatic change in the development of brines to the potash stage

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete