onset of aridity and dune building in central australia sedimentological and magnetostratigraphic evidence from lake amadeus abstract sediments from lake amadeus a groundwater discharge playa in central australia comprise a surface playa sequence the winmatti beds varying between 0 6 and 3 m in thickness overlying a long sequence of fairly uniform fluvial lacustrine clays the uluru clay the latter extends down to at least 15 m the maximum depth cored during this study and possibly down to 65 m below the present playa surface in the cores studied the brunhes matuyama boundary 0 73 ma was identifiable in all the upper sediments typically at a depth of between 1 and 2 m but below this there are two plausible chronological interpretations of the palaeomagnetic data deposition rates are very low typically no more than 1 5 cm ka in the uluru clay beds and down to 0 2 cm ka in the winmatti beds these rates suggest that the fluvial lacustrine phase lasted for at least 5 ma the boundary between the uluru clay and the winmatti beds bears a close correspondence to the boundary between the blanchetown clay a lacustrine sequence and the tyrrell beds a playa sequence in palaeo lake bungunnia in what is now the murray basin in southeastern australia however the transition occurs at about 0 9 ma or possibly 1 6 ma at lake amadeus whereas it has been dated palaeomagnetically at less than 0 73 ma probably 0 5 ma in lake bungunnia records from other locations in southeastern australia likewise support a major change from wetter to drier conditions at or shortly after the matuyama brunhes polarity transition thus the current evidence from lake amadeus indicates that in central australia the onset of aeolian and saline gypseous deposits characteristic of arid zone facies may have pre dated the corresponding change in the southeastern part of the continent by about 0 4 ma or possibly by about 1 1 ma in common with most playas in central australia lake amadeus is surrounded by a ring of gypseous dunes derived from material deflated from the surface of the playa magnetostratigraphic evidence from auger island in the middle of lake amadeus suggests that the oldest gypseous dune formation on the island must have pre dated the start of the jaramillo subchron at 0 98 ma or possibly the start of the brunhes epoch 0 73 ma thus making these the oldest dated dunes in australia the age of the auger island dunes is probably characteristic of other gypseous dunes around the margins of playas in central australia

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

palaeogeographic climatic and tectonic change in southeastern australia the late neogene evolution of the murray basin the murray basin is a low lying but extensive intracratonic depocentre in southeastern australia preserving an extraordinary record of late neogene sedimentation new stratigraphic and sedimento logic data allow the long term evolution of the basin to be re evaluated and suggest a significant role for 1 tectonism in controlling basin evolution and 2 progressive and step wise climatic change beginning in the early pleistocene tectonic change is associated with regional uplift occurring at approximately the same rate from the early pliocene until the present day and possibly associated with changing mantle circulation patterns or plate boundary processes this uplift led to the defeat and re routing of the murray river australia s major continental drainage system key to our interpretation is recognition of timing relationships between four prominent palaeogeographic features the loxton parilla sands strandplain the gambier coastal plain palaeo megalake bungunnia and the kanawinka escarpment geomorphic and stratigraphic evidence suggest that during the early pliocene the ancestral murray river was located in western victoria flowing south along the douglas depression relatively small amounts of regional uplift 200 m defeated this drainage system dramatically changing the palaeogeography of southeastern australia and forming plio pleistocene megalake bungunnia at its maximum extent lake bungunnia covered more than 50 000 km 2 making it one of the largest known palaeo or modern lakes in an intracontinental setting magnetostratigraphic constraints suggest lake formation c 2 4 ma the formation of lake bungunnia influenced the pliocene coastal dynamics depriving the coastline of a sediment source and changing the coastal system from a prograding strandline system to an erosional one erosion during this period formed the kanawinka escarpment a palaeo sea cliff and one of the most prominent and laterally extensive geomorphic features in southeastern australia marine sediments c 800 ka to c 1 16 ma represent the time of re establishment of depositional coastal dynamics and of a permanent outlet for the murray river this age range is consistent with our best estimate of the age of the youngest lake bungunnia sediments and points towards an early pleistocene age for the demise of the lake system the youngest lake bungunnia sediment present on a number of distinct terraces suggests that progressive step wise climatic change played a role in the demise of the lake however in order for the ancestral murray river system to have been able to breach the pre existing tectonic dam it is likely that tectonic change and or temporarily enhanced discharge was also significant this scenario indicates that the modern murray river has only been in existence for at most 700 ka c 2010 elsevier ltd all rights reserved less

australian desert dune fields initiated with pliocene pleistocene global climatic shift development of continental aridity has been linked to late cenozoic global cooling but the evidence is indirect based on terrestrial loess deposits and eolian silt in marine sediments whereas direct dating of the inception of arid landforms has been frustrated by a lack of suitable methods here we report the first age determination of a major arid zone dune field based on cosmogenic 10 be and 26 al measurements of drill cores from dunes in the simpson desert central australia results show that the dune field began to form ca 1 ma whereas dating using quartz optically stimulated luminescence indicates episodic dune building during late quaternary ice ages less intense desertification began earlier the previous cosmogenic exposure dating showed that neighboring stony deserts began to form at the onset of quaternary ice ages 2 4 ma aridity deepened and the dune field formed when ice age cycles increased their amplitude and switched their periods from 40 k y to 100 k y ca 1 ma

two stage mid brunhes climate transition and mid pleistocene human diversification abstract global climate shifted to markedly warmer interglacial conditions across the mid brunhes transition mbt 400 ka however a global mbt synthesis that spans marine and terrestrial evidence remains elusive which limits our understanding of the role of the mbt in mid pleistocene human evolution we synthesize asian precipitation reconstructions within a context of global palaeoclimatic records and find that the mbt occurred in two stages first stronger warming of northern hemisphere continents weaker southern hemisphere warming and related more extensive northward displacement of the intertropical convergence zone itcz during interglacial marine isotope stage mis 13 intensified and expanded precipitation in asian monsoon regions and in other widespread northern hemisphere regions with accompanying carbon reservoir changes featuring globally high marine benthic 13c values because of vegetation expansion at 500 ka subdued southern hemisphere warming and northward itcz displacement decreased southern hemisphere precipitation simultaneously during mis 13 second a shift to globally warmer interglacials at 400 ka with elevated atmospheric co2 concentrations smaller ice volume and higher sea level resulted in sustained high interglacial precipitation in east asia from mis 11 onward and sustained high marine benthic 13c values during mis 11 we also synthesize palaeoanthropological data and find that the climate and ecosystem changes across the mbt coincided with the timing of human lineage diversification including the emergence of neanderthals and denisovans in eurasia and homo sapiens in africa and their potential coexistence with h heidelbergensis h erectus h floresiensis h naledi and other homo archaics the timing of the mbt also coincided with novel hominin behavioural developments including fire control and the transition from handaxe industries to more versatile levallois techniques combined with environmental theories of human evolution this chronological coincidence suggests a potential link between mid pleistocene environmental changes and human evolution

mineral magnetic tracing of aeolian dust in southwest pacific sediments abstract reliable magnetic signatures were sought to trace aeolian dust in tasman sea sediments where the aeolian fraction had also been chemically isolated modern dust samples from eastern australia were found to have a strong ferrimagnetic signal and a weaker antiferromagnetic afm background the ferrimagnetic component could not be detected in the deep sea sediments where a finer biogenic magnetite component prevails over a background afm and two other authigenic components the modern dust is thought to be unrepresentative of prehistoric dust probably as the result of contamination from local agricultural soils the afm component in the sediments however was found to be highly correlated with the independently determined aeolian concentration except in intervals with a high magnetic susceptibility high fd signal possibly from an authigenic component because of the non aeolian contribution to magnetic hardness sirm irm 300 and different relationships observed in different cores the magnetic tracing of aeolian dust is currently only valid as a measure of relative changes in concentration in sediments with similar chemistry and low frequency dependence of susceptibility

chronology of murrumbidgee river palaeochannels on the riverine plain southeastern australia four major periods of palaeochannel activity have been identified on the murrumbidgee sector of the riverine plain of southeastern australia on the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle the ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments these are named the coleambally phase which occurred from 105 to 80 ka the mid to latter part of oxygen isotope stage 5 the kerarbury phase from 55 to 35 ka stage 3 the gum creek phase from 35 to 25 ka late stage 3 to early stage 2 and the yanco phase from 20 to 13 ka late stage 2 the present flow regime was established by about 12 ka stage 1 the first two phases correlate with episodes of enhanced fluvial activity in northern and central australia and with reduced dust activity globally the phases in stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the last glacial maximum source bordering aeolian dunes associated with the coleambally kerarbury and yanco phases were found however the tl dates show that some have undergone aeolian reworking thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of late quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here

magnetic polarity stratigraphy of the fisherman s cliff and bone gulch vertebrate fossil faunas from the murray basin new south wales australia abstract the fisherman s cliff and bone gulch local faunas are the second and third oldest mammalian fossil assemblages known in the murray basin of southeastern australia the determination of well constrained ages for these two faunas has been plagued by a lack of diagnostic microfossils or material suitable for isotopic age determinations based on previous paleomagnetic data 1 2 the ages of the fisherman s cliff and bone gulch local faunas were assigned to the gauss and lower matuyama chrons respectively however these dates were not tested by direct magnetostratigraphic studies at either locality in order to make direct correlations 22 paleomagnetic and five paleomagnetic sites respectively were collected from fisherman s cliff and bone gulch results indicate that the fisherman s cliff local fauna occurs within a zone of normal magnetic polarity whilst the bone gulch local fauna occurs within a zone of reversed polarity by correlation to the chowilla section these zones are interpreted to represent the gauss and lower matuyama chrons and ages of 2 47 2 92 and 1 88 2 47 myr are indicated for the fisherman s cliff and bone gulch local faunas respectively

quaternary stratigraphy geochronology and evolution of the magela creek catchment in the monsoon tropics of northern australia abstract magela creek a major tributary of the east alligator river in northern australia has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with quaternary glacial interglacial cycles uranium series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early pleistocene or tertiary time inset within this older alluvium is a valley fill which from thermoluminescence dates was initiated about 300 kyr ago with each glacial climate change and associated fall in sea level distinct palaeochannels have been eroded into these floodplains infilling later with alluvium when climate and base level conditions were conducive to fluvial deposition radiocarbon dates show that the most recent palaeochannel beneath the modern magela creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr the palaeochannel filled at an accelerating rate probably as a result of declining stream competence associated with drier conditions in the late holocene augmented by the backwater effects of sea level rise continued aggradation blocked the mouths of tributary valleys along magela creek forming alluvial dammed tributary lakes and deferred junction tributary streams from about 300 kyr cyclic episodes of channel incision and sediment evacuation in this tropical monsoon river valley have become less effective possibly because increasing aridity in the late quaternary has reduced the erosional effectiveness of australia s northern rivers reduced flow regime and rising sea level in the late holocene has resulted in the latest phase of alluvial accretion

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

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

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

palaeomagnetic stratigraphy of lake bungunnia plio pleistocene precursor of aridity in the murray basin southeastern australia abstract the murray darling river system in southeastern australia formerly flowed into a large lake lake bungunnia before reaching the sea fine grained clastics of this system the blanchetown clay formation extend over an area of about 68 000 km2 underlying the mallee region with its surface array of dunes and salt lakes palaeomagnetic analyses are used to date the major hydrologic transition from the expansive freshwater system to the saline deflation playas and dunes that characterize this landscape today two sites were selected for sampling one a cliff section on the left bank of the murray river at chowilla the other from within sediments of lake tyrrell a saline playa cut into sediments of the older freshwater system two sequences were sampled at tyrrell one by coring to 30 m in the basin centre the other a composite cliff and 5 m core on the western margin of the playa post bungunnia sediments representing modern landforms were sampled in both surficial dune palaeosol units of the woorinen formation and in saline sediments the tyrrell beds within the modern saline playa the sequence of multiple aeolian units of the woorinen formation and gypseous sediments of the tyrrell beds are normally magnetized indicating deposition within the past 0 7 million years by contrast the uppermost horizons of bedded blanchetown clay below a surface zone of pedogenic alteration are reversed the brunhes matuyama b m boundary key to the age of draining of lake bungunnia by deepening the overflow channel to the sea is obscured within the zone of pedogenesis separating unaltered blanchetown clays from overlying aeolian deposits the onset of aeolian and saline gypseous deposits characteristic of the arid zone facies is placed soon after the b m boundary about 500 000 years ago sequences through the blanchetown clay pass down through the matuyama reversed chron into the gauss normal chron with the lowermost section on the tyrrell west bank recording a basal reversed zone of possible gilbert age thus the origins of lake bungunnia extend back beyond basal pleistocene into the late pliocene the lake s duration covers more than 2 million years spanning the plio pleistocene boundary in this important region of southeastern australia

quaternary soil salinity events and australian vegetation history abstract a late quaternary history of australian soil salinization is produced by comparing chenopodiaceae and casuarina pollen curves although salinity development varied between sites its occurrence was generally associated with arid phases and when high rainfall or high sea level caused regionally high groundwater tables soil salinization contributed to the shift from casuarina to eucalyptus dominance of interglacial sclerophyll vegetation the deposition of saline sediments deflated from the murray basin seems more likely than aboriginal burning to have caused the decline of casuarina at lake george soil salinization probably resulted in other vegetation changes and must be taken into account in environmental reconstructions the renewed increase in soil salinity caused by european land use practices and an associated decline in casuarina are evident in the pollen records of many sites

14c analysis of aliphatic hydrocarbon fractions from the hypersaline lake tyrrell southeast australia conventional biomarker studies typically interpret the distribution structure and stable isotopic e g 13c d composition of sedimentary hydrocarbons and polar compounds however compound and compound class specific 14c analysis csra is becoming increasingly relevant for characterising millennial scale residence and mobilisation of sedimentary organic carbon oc here the 14c content of the aliphatic and bulk fractions from shallow cores from the hypersaline playa lake tyrrell southeast australia were compared the aliphatic hydrocarbon fractions predominantly n alkanes were substantially older than the corresponding bulk fractions indicating the presence of active reservoirs of ancient carbon likely derived from aeolian reworking of sediments the 14c ages of the aliphatic hydrocarbons in the core revealed two noticeable shifts in age and source of ancient oc that were not apparent using biomarker composition and sedimentology alone the study shows that aliphatic hydrocarbons are relatively simple to isolate even from organically lean ca 0 05 toc terrestrial sediments and their 14c ages yield information about carbon mobilisation and preservation not amenable to conventional analysis

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

late quaternary lake level changes and climates of australia abstract spatial and temporal patterns in lake level data from 38 sites in australia and papua new guinea provide a basis for reconstructing changes in water balance and atmospheric circulation during the past 30 000 years the reconstructions are consistent with hydrological changes inferred from pollen analysis and palaeowind directions inferred from dunes generally wetter conditions between 30 000 and 24 000 bp are consistent with a strong walker circulation with the sta near its present position general aridity at the glacial maximum until 12 000 bp with higher than present lake levels in the southeastern interior of australia implies that the southern margin of the subtropical anticyclone belt was expanded southward and the southern westerlies were correspondingly displaced this southward shift appears in all gcm simulations of the 18 000 bp climate and may be a result of the increased vigour of the northern hemisphere circulation a northward migration of the belt of high lake levels between 11 000 and 6000 bp suggests that the sta shifted back equatorward to north of its present position relaxation to modern conditions occurred after 6000 bp interrupted by an unexplained dry phase 6000 5000 bp in tasmania and queensland

tectonism and eustasy across a late miocene strandplain the loxton parilla sands murray basin southeastern australia abstract sediments of the loxton parilla sands form a progradational strandplain that stretches for over 350 km across the murray basin in southeastern australia the strandplain comprises over 600 individual ridges with stratigraphic and strontium isotope data indicating these strandlines are late miocene to early pliocene in age with deposition beginning before 7 2 ma and terminating at approximately 5 0 ma post pliocene uplift along the padthaway high due to regional compressive intraplate tectonism was responsible for altering the orientation of strandlines and drainage systems as well as contributing to increased erosion across the strandplain this uplift both restricted and starved the coastline of sand sized sediment changing the depositional environment from one of progradation to active erosion this produced a series of scarps along the southwestern murray basin and ultimately contributed to the formation of the kanawinka escarpment a large erosional cliff feature whose formation was not exclusively the result of fault related tectonism this evidence for pliocene tectonism along southeastern australia together with the depositional ages inferred from strontium isotope analysis indicates that contrary to previous work the strandlines of the loxton parilla sands do not represent an unbroken record of late miocene pliocene glacioeustatic change we estimate that approximately 3 ma of depositional history may be missing from the sedimentary record between the southwestern most loxton parilla sands strandlines and those of the pleistocene bridgewater formation

lake bungunnia a plio pleistocene megalake in southern australia abstract between 2 5 ma and 0 7 ma a plio pleistocene megalake lake bungunnia existed in the western murray basin australia study of hydrologic and geologic constraints on this lake has enabled the climate of southeastern australia during the late pliocene and early pleistocene to be partly quantified modelling shows that lake bungunnia could not exist under current climatic conditions and that an average rainfall of at least 500 mm yr 1 over the catchment of the murray darling river system was likely considerably more than at present minor changes in climate caused large fluctuations in the shoreline of the shallow lake which are reflected in the geologic record possible histories for lake bungunnia are suggested in the light of this evidence demise of the megalake heralded the onset of aridity in southern australia and modern landforms date from that time salt lakes in part of the western murray basin may have directly descended from lake bungunnia

radiocarbon dating of playa lake hydrologic changes examples from northwestern china and central australia accurate radiocarbon dating of arid zone playas is restricted by shortage of suitable organic matter analyses from two large systems in australia lake frome and china qarhan playa in the qaidam basin demonstrate the problems associated with the use of carbonates for dating organic carbon although requiring treatment of large samples 1 2 kg provides the most accurate basis for establishing chronologic control in qarhan a deposit of halite averaging about 30 m thick extends over an area of 5800 km2 carbonate in the system is dominantly derived as clastics from loess transported by northwesterly winds the large component of dead carbon thus involved explains anomalous patterns of dates derived from these materials such results are consistently much older than those based on organic carbon in lake frome subject to a more maritime climate in central australia the carbonate component is dominantly authigenic lacustrine in origin contaminated by a small detrital component it provides ages about one half life older than those from organic carbon the sequence from qarhan supplemented by evidence of lacustral pluvial episodes in two other sub basins in qaidam kunteyi and xiao qaidam illustrates the presence there of expanded waterbodies persisting from at least 40 000 to about 15 000 yr b p in areas where little surface water persists today the large evaporite deposits formed between about 25 000 to sometime after 15 000 yr b p holocene climate appears to have remained hyperarid like that of today at lake frome an early lacustral phase gave way before 18 000 yr b p to drying and aeolian activity water had returned to the system by 16 000 yr b p signalling a decline if not the end of aridity lacustrine conditions persisted through early holocene with drying and development of playa facies about 7000 yr b p after a brief return to lacustrine conditions between about 6000 4000 yr b p a dry playa environment has continued to the present day the frome and qarhan playas although in comparable latitudes lie in very different climatic and tectonic settings their palaeohydrologic records are neither in phase nor in distinct anti phase emphasizing the complexity of comparing palaeoclimatic records from different circulation systems

subsurface flow in lowland river gravel bars geomorphic and hydraulic processes which form gravel bars in large lowland rivers have distinctive characteristics that control the magnitude and spatial patterns of infiltration and exfiltration between rivers and their immediate subsurface environments we present a bedform infiltration relation together with a set of field measurements along two reaches of the san joaquin river ca to illustrate the conditions required for infiltration and exfiltration of flow between a stream and its undulating bed and a numerical model to investigate the factors that affect paths and residence times of flow through barforms at different discharges it is shown that asymmetry of bar morphology is a first order control on the extent and location of infiltration which would otherwise produce equal areas of infiltration and exfiltration under the assumption of sinusoidal bedforms hydraulic conductivity varies by orders of magnitude due to fine sediment accumulation and downstream coarsening related to the process of bar evolution this systematic variability not only controls the magnitude of infiltration but also the residence time of flow through the bed the lowest hydraulic conductivity along the reach occurred where the difference between the topographic gradient and the water surface gradient is at a maximum and thus where infiltration would be greatest into a homogeneous bar indicating the importance of managing sand supply to maintain the ventilation and flow through salmon spawning riffles numerical simulations corroborate our interpretation that infiltration patterns and rates are controlled by distinctive features of bar morphology

subdividing the pleistocene using the matuyama brunhes boundary mbb an australasian perspective abstract the last major reversal of the earth s magnetic field the matuyama brunhes boundary mbb dated at 0 78 ma is widely identified in australian and new zealand pleistocene deposits in new zealand the mbb is precisely located in shallow marine sediments of wanganui basin where it corresponds with the base of the new zealand putikian substage a combination of marine biostratigraphy sequence stratigraphy and tephrostratigraphy permit correlation from wanganui basin to other on land sections and deep sea cores in australia the mbb is identified in many continental sequences particularly saline lake basins however chemical weathering has resulted in variable brunhes age normal overprints that are sometimes difficult to remove australasian tektites are a potential lithostratigraphic marker just prior to the mbb but have yet to be identified in the same on land section as the mbb in australia identification of reverse polarity magnetisation in weathered deposits including soils provides a minimum age of 0 78 ma for these materials a widespread arid shift in paleoclimate succeeded the mbb in australia placement of the lower middle pleistocene boundary at the mbb would constitute the most recognisable chronostratigraphic marker in weathered continental deposits

magnetic polarity stratigraphy of the pleistocene section at portland victoria australia abstract three to seven oriented paleomagnetic samples were collected from 16 sites in the nelson bay and bridgewater formations at portland victoria which contains the recently discovered nelson bay local fauna l f the entire section has reversed polarity these results along with globorotalia truncatulinoides within the section and the presence of underlying middle pliocene dated basalts indicate that the portland section and the included nelson bay l f was deposited within the late matuyama chron between 1 66 and 0 73 myr ago this represents the first well documented pre 14c pleistocene mammalian fauna in australia calibrated in direct stratigraphic context with absolute dating methods in addition the reversed polarity for the bridgewater formation confirms the previous hypothesis that the depositional history of this beach sand deposit is time transgressive across the brunhes matuyama boundary

paleosols in laterite and silcrete profiles evidence from the south east margin of the australian precambrian shield abstract laterite and silcrete profiles are common in the arid and semi arid areas of the australian precambrian shield a vast planar surface masked by the regolith much of the geological history of the shield subsequent to its early development is recorded in ancient cover rocks and younger basin sediments which occur in important stratigraphic sequences particularly on the margins of the shield within these sequences stratigraphically associated or as companion materials weathering zones and paleosols were developed which individually and as assemblages of layers and horizons record the history of weathering and of soil formation since the proterozoic laterite and silcrete profiles are seen to be assemblages of paleosols stratigraphically associated deposits and companion materials which were formed in response to changes in groundwater conditions at particular times in the past the paleosols record the evolution of the regolith older weathering zones and bleached rocks were features of successive landscapes after the early palaeozoic ferruginous mottling ferricrete and silcrete pans were formed after the early cainozoic ferricretes and mottled clay paleosols some of which have been described as laterite were formed during and after the pliocene materials in laterite and silcrete profiles are overlain in places by calcretes formed after the early pleistocene and by younger soils the assemblages are distinctive and are characteristic of particular morpholithogical provinces

the effect of 3 d structure on lg propagation patterns the method of ray diagrams based on the constructive interference of multiple s reflections gives a visual measure of the interaction of guided wavetrains with variations in crustal structure the technique is extended to 3 d heterogeneity and by representing the s ray systems in plan view through their basement reflection points a semi quantitative measure of the disruption of lg at different phase velocities can be made in addition the tilt of the ray systems can be used as an indication of the degree of interconversion between rayleigh and love wave energy two simple crustal models are examined to investigate the effects of oblique incidence and transverse topographic gradients on multiple s reflections using ray diagrams the method is then applied to several real earth models of the crust in central asia using topographic data and assuming isostasy interpretations of the ray diagrams for paths across the major tectonic features compare well with many of the observations from previous studies ruzaikan et al 1977 ni barazangi 1983 and suggest that the gross characteristics of lg propagation can be attributed to the shape of the crustal waveguide

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

stratigraphic architecture resulting from late quaternary evolution of the riverine plain south eastern australia the riverine plain of south eastern australia is the result of prolonged cenozoic fluvial activity single thread anabranching and distributary channels and floodplains and associated aeolian dunes characterize the uppermost sequences based on detailed interpretations of late quaternary fluvial sedimentation and surficial stratigraphy for this 77 000 km2 basin earlier prior stream and ancestral stream models of fluvial deposition deduced from limited stratigraphic and chronological evidence are replaced with aggradational palaeochannel and migrational palaeochannel models thermoluminescence dating reveals four distinct phases of palaeochannel activity between 105 and 12 ka the first coleambally phase late in oxygen isotope stage 5 the second kerarbury phase in stage 3 the third gum creek phase before and the fourth yanco phase after the last glacial maximum lgm in stage 2 the first three of these phases were characterized by mixed load laterally migrating sinuous palaeochannels with occasional transitions to a straighter bedload dominated mode and vice versa the first two phases concluded with a bedload dominated episode resulting in aggradational palaeochannels on the surface of the plain and the third phase prior to the lgm did also in its downstream reaches the phase following the lgm was characterized entirely by large mixed load sinuous migrational palaeochannels these exhibited no terminating bedload episode because the onset of holocene climates reduced the size of the flood peaks greatly diminished the supply of bedload from the upper catchments and resulted in streams evolving to their present highly sinuous suspended load form the result is a complex stratigraphic architecture consisting of vertically and laterally accreted units extending over hundreds of kilometres in the form of channel sand stringers sand sheets and derivative aeolian dunes partially or wholly encased in overbank fines

indonesian throughflow drove australian climate from humid pliocene to arid pleistocene late miocene to mid pleistocene sedimentary proxy records reveal that northwest australia underwent an abrupt transition from dry to humid climate conditions at 5 5 million years ma likely receiving year round rainfall but after 3 3 ma climate shifted toward an increasingly seasonal precipitation regime the progressive constriction of the indonesian throughflow likely decreased continental humidity and transferred control of northwest australian climate from the pacific to the indian ocean leading to drier conditions punctuated by monsoonal precipitation the northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by 2 4 ma well after the intensification of northern hemisphere glaciation the transition from humid to arid conditions was driven by changes in pacific and indian ocean circulation and regional atmospheric moisture transport influenced by the emerging maritime continent we conclude that the maritime continent is the switchboard modulating teleconnections between tropical and high latitude climate systems

responses of quaternary rainforest vertebrates to climate change in australia a new previous termmiddle pleistocenenext term vertebrate fossil record from eastern australia dated by u disequilibrium series records the first quaternary record of an australian tropical rainforest fauna this exceptionally rich fauna underwent extinction after a long period of relative faunal stability spanning several glacial cycles and persisted probably until 280 000 years ago some time between 280 000 and 205 000 years ago the rainforest fauna was replaced by a xeric adapted fauna since that time the xeric adapted fauna was replaced by a mesic adapted fauna which was established by the holocene this is the first vertebrate faunal evidence in australia of the previous termmiddle pleistocenenext term mid brunhes climatic event mbe a major climatic reorganisation that led to increased aridity in northern australia from around 300 000 years ago several independent palaeoclimate proxies suggest that the climatic shift to aridity was due to increased climatic variability and weakened northern monsoons which may be manifested in the extinction of the aseasonal rainforest fauna and its replacement by an arid adapted fauna we extend the temporal ranges of several taxa from the pliocene into the previous termmiddle pleistocene next term we also reveal a longer palaeobiogeographic connection of rainforest taxa and lineages shared between new guinea and australia than was previously thought and show that their extinction on mainland australia occurred sometime after 280 000 years ago

geomorphology stratigraphy and thermoluminescence dating of the lunette dune at lake victoria western new south wales abstract lake victoria 13 km long and 10 km wide is the largest lunette lake attached to the murray river in southeastern australia the lake occupies the western part of a larger basin at least twice the size of the present lake the larger basin has been incised nearly 30 m into the regional sand plain surface and into the early middle pleistocene blanchetown clay within the larger basin east of the lunette of the present lake victoria various landforms have developed including alluvial terraces salt pans small dry basins and multiple small lunettes among these an arcshaped sand ridge possibly an old lunette was dated by tl as 82 ka the present lunette of lake victoria is up to 40 m high and consists of 3 units nulla nulla sand 30 m thick talgarry sand up to 10 m thick and the reworked dunedin park sand the nulla nulla sand consists dominantly of pure medium to fine grained sand sequences with a few red palaeosols indicating long standing high lake levels with a few lunette stable intervals deposition of the nulla nulla sand ended around 20 ka starting at least 40 ka ago and probably much earlier the talgarry sand overlying a prominent red palaeosol on top of the nulla nulla sand consists of pure sand horizons interbedded with at least 3 gypseous clayey silt layers the gypseous sediments indicate a major change of hydrologic conditions in the lake basin fluctuation of lake levels and periodically high salinity the talgarry sand was deposited from 17 to 10 ka as dated by tl and previous 14c dates after 10 ka lunette accretion stopped possibly the result of incision of the murray river channel reducing the water and sediment input to the basin however erosion and deflation of the lunette formed an apron of sediment on the lower lake facing slope and sand transport to the lee side long slope leaving islands of old sediment along the lunette crest zone

the norwest bend formation implications for the evolution of neogene drainage in southeastern australia abstract strontium isotope data indicate that sediments of the norwest bend formation were deposited within a large estuarine system during the latest miocene to early pliocene probably 5 ma the norwest bend formation is divisible into two members a lower sand dominated member and an upper oyster coquina member these two units are separated by an irregular erosion surface that has no correlative within the adjacent loxton parilla sands tectonism in the western murray basin adjacent to the adelaide foldbelt has exerted a considerable control over the formation of these estuarine sediments the lower norwest bend formation occupies a paleodrainage system that was restricted to a region west of the hamley fault and was presumably incised following uplift of this western block flooding of this paleodrainage system produced the lower norwest bend estuarine system later tectonism on the hamley fault resulted in the formation of the erosion surface within the norwest bend formation we suggest that the norwest bend estuarine system owes its existence to marginal tectonism associated with the young uplift of the mt lofty flinders ranges the paleodrainage system incised prior to deposition of the norwest bend formation differs markedly in geometry from the present murray river gorge system this suggests that the modern murray river system developed after deposition of the late miocene pliocene norwest bend formation