evaluation of simple geochemical indicators of aeolian sand provenance late quaternary dune fields of north america revisited abstract dune fields of quaternary age occupy large areas of the world s arid and semiarid regions despite this there has been surprisingly little work done on understanding dune sediment provenance in part because many techniques are time consuming prone to operator error experimental highly specialized expensive or require sophisticated instrumentation provenance of dune sand using k rb and k ba values in k feldspar in aeolian sands of the arid and semiarid regions of north america is tested here results indicate that k rb and k ba can distinguish different river sands that are sediment sources for dunes and dune fields themselves have distinctive k rb and k ba compositions over the basin and range and great plains regions of north america the hypothesized sediment sources of dune fields are reviewed and assessed using k rb and k ba values in dune sands and in hypothesized source sediments in some cases the origins of dunes assessed in this manner are consistent with previous studies and in others dune fields are found to have a more complex origin than previously thought use of k rb and k ba for provenance studies is a robust method that is inexpensive rapid and highly reproducible it exploits one of the most common minerals found in dune sand k feldspar the method avoids the problem of using simple concentrations of key elements that may be subject to interpretative bias due to changes in mineralogical maturity of quaternary dune fields that occur over time

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

the tectonic development of the western margin of the gulf of elat aqaba rift abstract along the western coast of the gulf of elat a 30 km wide shear belt of subparallel faults trending n s to ne sw is developed this shear belt is observed mainly within the precambrian basement terrain sinistral movements on these faults have been recognized based on offsets of magmatic bodies and lithological contacts in rocks of precambrian age the cumulative displacement measured independently at several localities across the belt attains a total of 24 km early neogene volcanism in the form of long dikes trending nw se is known from the eastern desert of egypt of the gulf of suez and along the red sea coast of saudi arabia volcanic bodies of a similar pattern have been identified in eastern sinai these bodies mainly dolerites and basalts intruding mesozoic sediments are parallel to each other and to the gulf of suez they are tens to hundreds of kilometers long and spaced several tens of kilometers apart dating k ar of bodies in sinai saudi arabia and in the eastern desert of egypt suggest an age of 20 22 m y for this extensive volcanism all the dikes are sinistrally displaced by the individual faults of the eastern sinai shear belt the amount of movement recorded using the precambrian markers is identical to movement recorded by offsets of the early neogene dikes this proves that the total 24 km shear of this fault system postdates the 20 22 m y volcanic phase it is assumed that the recorded movements are part of the 105 110 km shear persumed to exist along the gulf of elat which is also younger than 20 22 m y preliminary results suggest that a similar amount of movement is observable along a shear zone developed on the eastern coast of the gulf of elat thus only some 60 km movement are taken up by faults in the gulf itself the evolving model suggests that 1 a the intrusion of very long basaltic dikes in a nw se direction on both sides of the red sea accompanied the initial stage of development of the red sea gulf of suez rift valley 2 b a basic change in the geotectonic regime occurs after the intrusion of this volcanic suite large scale horizontal movements are initiated being recorded as a 105 110 km sinistral movement along the arava jordan rift this movement implies a synchronous opening of the red sea

new evidence for the timing of aeolian sand supply to the algodones dunefield and east mesa area southeastern california usa results are presented from a preliminary investigation undertaken to provide insight into the timing and causes of aeolian sand supply and dune dynamics within the east mesa algodones dunefield area of southeastern california samples for radiocarbon and optically stimulated luminescence osl dating were collected from a number of sites along a west east transect extending from the 12 m shoreline of palaeolake cahuilla to the central part of the algodones dunefield the western algodones dunefield is underlain by weathered aeolian sands which yielded an osl age of c 31 ka confirming earlier estimates of the timing of dunefield initiation these deposits are largely buried by unweathered aeolian sediments which gave osl ages of c 3 1 ka and 0 4 ka these ages correspond quite closely with radiocarbon and osl ages obtained from deposits within and immediately overlying the former lake shorelines providing support for the hypothesis that the shorelines acted as an important source of aeolian sediment dates from within the algodones suggest an average long term eastward movement of the dunefield of c 16 6 m ka 1 individual transverse megadunes are indicated to have moved southeastwards at an average rate of 2 5 m a 1 over the last 100 200 yr an order of magnitude higher than previous estimates based on process studies

translocated plio pleistocene drainage systems along the arava fault of the dead sea transform abstract geomorphic and sedimentologic field studies and analyses of landsat 5 images and topographic maps indicate 15 km of left lateral displacement of a pliocene large stream and alluvial fans along the dead sea transform in southern israel and jordan in the central arava valley a rift valley located along the transform there is a notable discrepancy between the number and location of the feeding drainage basins within the eastern margins of the arava valley and those of the alluvial fans and the cross rift large stream a few of these large alluvial fans lack any feeding drainage basin furthermore east of the large stream there is no drainage basin that could have fed it these discrepancies between the physiography locations sizes and lithological compositions of the feeding drainage basins and of the alluvial fans can be explained by 15 km of left lateral movement since the late pliocene or the early pleistocene along the arava dead sea segment of the transform this is one of the largest displacements of a landform and surficial alluvial deposit in the world however the resulting average long term rate of movement is relatively small 0 3 0 75 cm year

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

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

asymmetry and basin migration in the dead sea rift the dead sea depression sensu stricto forms the deepest continental part of the dead sea rift a transfer which separates the levanthine and arabian plates it is occupied by three distinct sedimentary bodies deposited in basins whose depocenters are displaced northward with time they are the continental red beds of the hazeva formation miocene the bira lido gesher marls and the exceptionally thick rocksalt of the sedom formation pliocene early pleistocene and the successive amora lisan and dead sea evaporites and clastics early pleistocene recent lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to leftlateral shear combined with anticlockwise rotation of the arabian eastern plate steeper faulting of the crustal eastern margin than of the western sedimentary margin and modification of depositional pattern by twice filling up of basins by hazeva red beds during late miocene pause of shear and by sedom rocksalt during pliocene marine ingression

sand supply to the algodones dunefield south eastern california usa in an effort to gain a better understanding of the relationship between climate sand supply and aeolian sand deposition an investigation was undertaken in the algodones dunefield of south eastern california to determine 1 the source of the sand and 2 the mode of sand supply to the algodones dunefield textural geochemical and mineralogical analyses show that the dune sands were mainly derived from colorado river sands during episodes when the colorado river drained west to the salton basin instead of south to the gulf of california a model is presented which relates episodic aeolian deposition in the algodones dunefield to the growth of the resulting lake under a persistent intense north westerly wind regime and to subsequent desiccation of the lake following diversion of the colorado river to the gulf of california late holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south western united states these conditions are likely to have been the cause of intensified north westerly winds which coincided with high stands of lake cahuilla although diversion of the colorado river to the salton basin occurred at least three times during the late holocene it is evident that the river did not change its course in response to the majority of the floods it appears that the critical control on diversion of the river was the difference in gradient between courses leading to the salton basin and gulf of california which in turn was influenced by fluvial deposition and tectonic activity flooding was able to cause diversion of the colorado river to the salton basin only when the difference in gradient between the two courses was relatively small

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

late pleistocene eolian history of the liwa region arabian peninsula the liwa region of the united arab emirates is one of the most distinctive geomorphological features of the rub al khali desert of southern arabia characterized by a sharp crescentic boundary coincident with a n s elevation drop of 65 m with the transverse ridges in al q fa to the north liwa is an area of some of the world9s largest megabarchan dunes deep drilling of continuous cores has provided an opportunity to observe the internal structure and age of these two ergs subsurface stratigraphy is complex reflecting rapid facies transitions between dune and interdune sub environments most of the cored sediment is dominated by cross bedded and structureless sand units of inferred eolian transverse dune depositional origin a total of 56 optical ages for sand sized quartz grains extracted from these cores provide a chronological framework for deposition of the late quaternary ergs a marine isotope stage mis 5 erg is identified north of the liwa crescent in the al q fa region which reaches vertical thicknesses 100 m a mis 1 erg in the form of megabarchan dunes is recorded south of the liwa crescent this was deposited on a pre mis 5 land surface since ca 6 ka over a period of just a few thousand years contemporary bypassing of eolian sands via superimposed dunes in both al q fa and liwa appears to be in equilibrium with the current wind regime a consideration of a variety of factors that control the availability mobilization and preservation of eolian sediments and resulting bedforms leads us to infer that the system is not sediment supply or transport limited instead the system is preservation limited being controlled by a correlated combination of sea level and precipitation both of these factors are strongly linked to global climate variations in the eccentricity ca 100 ka band paradoxically the bulk of the preserved record of eolian activity in the southern arabian peninsula occurs within relatively humid interglacial phases rather than arid intervals evidence of eolian deposition during arid phases may not for the most part be preserved in large areas of the sand sea observed contrasts in the preserved record of eolian activity between al q fa and liwa and the wahiba sand sea may in part relate to contrasting eolian bedform morphology

palynological evidence for the age and rate of sedimentation along the dead sea rift and structural implications abstract pollen diagrams obtained for eight deep boreholes penetrating the thick sequences of the dead sea rift fill correlated with dated marine sequences of the coastal plain in israel enable stratigraphie assignment of the continental deposits to be made the sedimentary units of the rift valley are of two main provenances those deposited in troughs within the rift limits of predominantly lacustrine environment attaining thicknesses in the order of 1 2 km for which the trough is the final erosion base level and those not limited to the rift boundaries but known from wide areas in israel mostly laid down in river systems that crossed the rift region on their way to the sea these fluviatile formations are in the order of hundreds of meters thick in the rift valley region which acted as an intermediate basin the first group of rock units of late miocene through early middle pliocene to glacial pleistocene ages indicate phases of considerable subsidence the earlier termed the erythrean and the later the levantine phase these are predated in the late oligocene through middle miocene by gentle subsidence and separated during the late pliocene preglacial pleistocene by another period of relative quietness in tectonic activity

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

a spreading episode at the southern end of the san andreas fault system the cerro prieto region of baja california mexico is one of the few locations in the world where on land spreading is indicated1 and represents a transition between the east pacific rise and the strike slip san andreas fault system fig 1 it is characterized by high heat flow and volcanic activity and contains one of the world s most closely monitored geothermal fields whose heat source is thought to be a magmatic body emplaced at 5 6 km depth2 cerro prieto is thus an excellent area in which to examine the spatial and temporal properties of the spreading process in detail here we present four lines of evidence that an on land spreading episode occurred at cerro prieto between 1979 and 1981 the occurrence of the imperial valley earthquake of 15 october 1979 and the victoria earthquake of 9 june 1980 both of which produced slip near cerro prieto extension in the expected nw se spreading direction both from direct measurements of areal strain and from the combined slip on the two faults subsidence of up to 25cm near the cerro prieto geothermal field from levelling and gravity data and an abrupt rise in temperature and hco3 concentration in the cerro prieto geothermal reservoir both of which indicate the presence of magma at depth3

sedimentary record of erg migration the sedimentary record of erg eolian sand sea migration consists of an idealized threefold division of sand sea facies sequences the basal division here termed the fore erg is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment these sand bodies consist of eolian strata deposited by small dune complexes zibars and sand sheets the fore erg represents the downwind leading edge of the erg and records the onset of eolian sedimentation basin subsidence coupled with erg migration places the medial division termed the central erg over the fore erg strata the central erg represented by a thick accumulation of large scale cross stratified sandstone is the product of large draa complexes eolian influence on regional sedimentation patterns is greatest in the central erg and most of the sand transported and deposited in the erg is contained within this region reduction in sand supply and continued erg migration will cover the central erg deposits with a veneer of back erg deposits this upper division of the erg facies sequence resembles closely the fore erg region similar types of eolian strata are present and organized in sand bodies encased in sediments of the upwind flanking depositional environment s back erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration or they may be completely absent because of great susceptibility to postdepositional erosion tectonic climatic and eustatic influences on sand sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence the resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western north america europe southern africa and south america

climbing zibars of the algodones abstract zibars are coarse grained low relief slipfaceless eolian bedforms that occur on sand sheets and within interdune corridors of many eolian sand seas zibar surface features consist exclusively of wind ripples and local shadow and shrub coppice dunes associated with vegetation a study of zibars located on the southwestern margin of the algodones dune field california shows that zibars and their associated interzibar areas are migrating features oriented transverse to oblique to the resultant sand transport direction zibars leave deposits formed by deposition on the zibar lee face the zibar shape modifies the near surface airflow to produce a subtle grain size change across the zibar interzibar surface flow expansion not separation leeward of the zibar crest causes the lee face deposits those preserved upon bedform migration to have the finest grain size on the zibar interzibar surface sediment coarser than that deposited on the zibar lee face is transported more slowly and less frequently and thus becomes concentrated on the zibar stoss slope and ultimately becomes interzibar deposits migration of zibars and interzibar areas can produce two characteristic depositional sequences depending upon the angle of climb for low angles of climb a sequence of stacked amalgamated interzibar deposits is preserved zibar deposits are absent amalgamated interzibar deposits consist of low angle usually less than 5 wind ripple laminae of medium to coarse sand given higher angles of climb deposits of both the entire interzibar and zibar lower lee face are preserved low angle interzibar deposits of medium to coarse sand are overlain tangentially by finer grained fine to medium sand wind ripple laminae dipping less than 15 of the zibar lee face lee face wind ripple laminae are sharply truncated and overlain by the succeeding set of interzibar wind ripple deposits this zibar interzibar sequence is distinctive and allows for the detailed interpretation of some ancient sand sheet deposits as left by migrating zibars a possible example of ancient zibar deposits is present in the entrada sandstone jurassic of southwestern colorado

an empirical model of aeolian dune lee face airflow airflow data gathered over dunes ranging from 60 m tall complex crescentic dunes to 2 m tall simplecrescentic dunes were used to develop an empirical model of dune lee face airflow for straight crested dunes the nature of lee face flow varies and was found to be controlled by the interaction of at least three factors dune shape the incidence angle between the primary wind direction and the dune brinkline and atmospheric thermal stability three types of lee face flow separated attached and deflected along slope or attached and undeflected were found to occur separated flows characterized by a zone of low speed 0 3o of crestal speed back eddy flow typically occur leeward of steep sided dunes in transverse flow conditions unstable atmospheric thermal stability also favours flow separation attached flows characterized by higher flow speeds up to 84 of crestal speed that are a cosine function of the incidence angle typically occur leeward of dunes that have a lower average lee slope and are subject to oblique flow conditions depending on the slope of the lee face attached flow may be either deflected along slope lee slopes greater than about 20 or have the same direction as the primary flow lee slopes less than about 20 neutral atmospheric thermal stability also favours flow attachment as each of the three types of lee face flow is defined by a range of wind speeds and directions the nature of lee face flow is intimately tied to the type of aeolian depositional process i e wind ripple or superimposed dune migration grainflow or grainfall that occurs on the lee slope and the resulting pattern of dune deposits therefore the model presented in this paper can be used to enhance the interpretation of palaeowind regime and dune type from aeolian cross strata

a preliminary study of the dynamics of a modern draa algodones southeastern california usa a transverse crescentic draa in the algodones dune field california was monitored for a year using surface process mapping aerial photography and supplemental wind measurement the draa is oriented by the long term resultant wind whereas its superimposed features are in equilibrium with the bedform modified secondary airflow surface airflow and the movement of superimposed bedforms is typically oblique or parallel to the draa brinkline particularly on the lee slope comparison of measurements of draa movement and sand deposition on the lee slope with expected rates calculated from wind data and draa size confirm that there is a significant component of sand flow parallel to the draa brinkline the internal structure being generated at the base of the draa lee slope is inferred from the surface processes active there within the space of a kilometer two types of compound cross strata separated by an area of simple cross strata are being produced this has significant implications for interpretations of ancient aeolian strata variations in internal structure types found in lateral sequence may be generated by one complex bedform and these cross strata may be simple or compound second order bounding surface orientations indicate resultant primary palaeowind directions compound cross strata dip directions indicate secondary flow conditions the existence of cross strata dip directions oblique or perpendicular to the second order surface indicates longitudinal secondary flow on the lee face but not necessarily a longitudinal or oblique draa without further detailed knowledge about various draa configurations and behaviour stratification attributed to draas can be used only to interpret activity on the lower draa lee face

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

luminescence dating applications in geomorphological research abstract chronological control remains critical to the interpretation of environmental change and to establishing long term rates of geomorphological processes radiocarbon dating will continue to be the central technique for age assessment of carbon bearing sediments deposited in the last ca 40 ka but alternative absolute dating strategies are required for older or non carbon bearing sediments they include uranium series dating of precipitated sediments k ar and ar ar dating of primary volcanic materials and cosmogenic isotopic dating of surface exposure ages an additional family of methods collectively termed luminescence techniques is increasingly providing a basis for the age assessment of detrital sedimentary deposits these methods directly date the deposition of detrital mineral grains typically quartz and feldspar and have been demonstrated to provide accurate deposition chronologies for up to 800 ka although 150 ka is more typical in the past decade a subset of luminescence techniques which employ optical sample stimulation methods called optical dating has made it possible to date samples from a much wider range of depositional systems given that the methods directly date sedimentation they allow direct assessment of depositional dynamism in numerous terrestrial and subaqueous including marine sedimentary systems and have demonstrated particular potential in the elucidation of chronologies from aeolian dune and loess fluvial colluvial coastal and volcaniclastic environments this paper provides a summary of the principles of the luminescence especially optical dating methods and shows how recent developments specifically single aliquot dating procedures have dramatically enhanced the scope and potential of the method the luminescence techniques are increasingly being incorporated into a wide range of geomorphological studies which seek to establish the nature of landscape changes over the past interglacial glacial cycle and beyond

optical dating of young modern sediments using quartz results from a selection of depositional environments abstract equivalent dose ed evaluations for quartz grains extracted from a number of modern or young samples collected from a range of depositional environments are reported the signal used was optically stimulated luminescence osl with an argon ion laser tuned to 514 nm as a light source typical equivalent dose values were 0 05 0 3 gy for the given samples which is substantially less than equivalent doses expected for similar sediments by conventional thermoluminescence tl the non zero equivalent dose exhibited by the samples may be a product of relict osl from incompletely bleached traps sample pre treatment procedures or due to signal recuperation following bleaching during antiquity the potential significance of each are discussed a number of modifications to sample pre treatment and processing are also described

late quaternary alluvial fans at the eastern end of the san bernardino mountains southern california abstract alluvial fans at the eastern end of the san bernardino mountains in southern california provide a record of climate modulated sediment transfer and erosion and are deformed and displaced in places by active faults alluvial fans within two study areas the mission creek and the whitewater river drainages were examined using geomorphic sedimentological and 10be terrestrial cosmogenic nuclide tcn surface exposure methods to define the timing of alluvial fan formation and erosion and to examine the role of climatic tectonic and autocyclic processes these alluvial fan complexes were studied because they are amongst the best preserved successions of alluvial fans in southern california and they are located at the mouths of two of the largest drainages whitewater river and mission creek in the san bernardino mountains and traverse major faults the mission creek and banning the alluvial fans comprise bouldery debris deposits that represent deposition dominated by flash flood and debris flow events tcn surface exposure dating indicates that abandonment incision of alluvial fan surfaces date to early in the last glacial or more likely the penultimate glacial cycle to marine isotope stage mis 4 and to the holocene the lack of alluvial fan ages during the latter part of the last glacial mis 2 and 3 suggests that there has been little alluvial fan lobe deposition incision during that time this is similar to findings for many other alluvial fans throughout the american southwest and supports the view that there is a strong climatic control on alluvial fan formation throughout this region furthermore the oldest alluvial fan surfaces in the mission creek region are beheaded by the whitewater river drainage showing that the oldest alluvial fans in the mission creek region underwent significant capture by the whitewater river drainage this shows the autocyclic controls are also important on alluvial fan evolution in this region but the importance of these processes to alluvial fan development in other regions of the american southwest needs to be more fully assessed the alluvial fans in the mission creek area traverse the mission creek fault but are not deformed by it which suggests that there may have been little if any movement along this fault since at least mis 4 in contrast alluvial fans in the whitewater river study are displaced by active faults highlighting the influence of tectonism on alluvial fan development in this region in addition to illustrating the importance of climatic controls on the development of alluvial fans in the american southwest a classic region for alluvial fan studies this study illustrates the complex mixture of autocyclic and allocyclic factors that force alluvial fan development in tectonically active settings

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

linking the tropical northern hemisphere pattern to the pacific warm blob and atlantic cold blob abstractduring 2013 15 prolonged near surface warming in the northeastern pacific was observed and has been referred to as the pacific warm blob here statistical analyses are conducted to show that the generation of the pacific blob is closely related to the tropical northern hemisphere tnh pattern in the atmosphere when the tnh pattern stays in its positive phase for extended periods of time it generates prolonged blob events primarily through anomalies in surface heat fluxes and secondarily through anomalies in wind induced ocean advection five prolonged 24 months blob events are identified during the past six decades 1948 2015 and the tnh blob relationship can be recognized in all of them although the pacific decadal oscillation and el nino can also induce an arc shaped warming pattern near the pacific blob region they are not responsible for the generation of pacific blob events the essential feature of pacific blob generation is the tnh forced gulf of alaska warming pattern this stu

algodones dune field of southeastern california case history of a migrating modern dune field the algodones dune field of southeastern california is one of the largest active dune fields in north america the dune field is migrating in an easterly direction oblique to the resultant sand flow direction s 24 e the migration of the algodones results from an interaction between regional winds and the dune field this interaction generates a localized secondary flow that has caused the dune field to migrate in a direction oblique to the resultant sand flow direction four lines of evidence suggest that the algodones has migrated in an easterly direction 1 a ramp interpreted as the trailing edge of the dune field 35 m thick and 500 m wide composed of aeolian deposits that borders the western edge of the dune field no similar deposits are found on the eastern leading edge margin of the dune field 2 leading edge sand sheet deposits are exposed in interdune areas within the dune field these deposits are west of the modern leading edge sand sheet 3 across the breadth of the dune field sands are consistently coarser and more poorly sorted in the west and finer and better sorted in the east this observation suggests that sand is transported from west to east 4 eastward migration of a large compound complex crescentic dune if the dune field continues to migrate it will deposit a vertical sequence consisting of a basal sand sheet deposit consisting of wind and water ripple laminae small scale aeolian cross strata and ephemeral stream wadi deposits aeolian dune deposits consisting of medium scale aeolian compound cross strata small scale simple sets of aeolian cross strata with highly variable dip directions a sand sheet containing low angle wind ripple cross strata capped by a coarse sand lag super bounding surface

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples