geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

calibration of the mdco dust collector and of four versions of the inverted frisbee dust deposition sampler abstract wind tunnel experiments were conducted to determine the efficiency of sediment samplers designed to measure the deposition of aeolian dust efficiency was ascertained relative to a water surface which was considered the best alternative for simulating a perfectly absorbent surface two types of samplers were studied the marble dust collector mdco and the inverted frisbee sampler four versions of the latter catcher were tested an empty frisbee an empty frisbee surrounded by an aerodynamic flow deflector ring a frisbee filled with glass marbles and a frisbee filled with glass marbles and surrounded by a flow deflector ring efficiency was ascertained for five wind velocities range 1 5 m s 1 and eight grain size classes range 10 89 m the efficiency of dust deposition catchers diminishes rapidly as the wind speed increases it also diminishes as the particles caught become coarser adding a flow deflector ring to a catcher substantially improves the catcher s efficiency by up to 100 in some cases the addition of glass marbles to a catcher on the other hand does not seem to increase the efficiency at least not at wind velocities inferior to the deflation threshold for higher velocities the marbles protect the settled particles from resuspension keeping them in the catcher the following five parameters determine the accumulation of aeolian dust in a catcher the horizontal dust flux the weight of the particles atmospheric turbulence resuspension and the dust shadow effect created by the catcher the final accumulation flux depends on the combination of these parameters the catchers tested in this study belong to the best catchers currently in use in earth science and have been the subject of various aerodynamic studies to improve their efficiency nevertheless the catching efficiency remains low in the order of 20 40 for wind speeds above 2 m s 1 other catchers suffer from the same low efficiencies there is thus evidence to believe that dust deposition rates published in the aeolian literature and obtained by collecting the sediment in a catcher largely underestimate the true deposition the errors are considerable of the order of 100 and more a reconsideration of the literature data on aeolian dust deposition measured by catchers is therefore required

last glacial maximum to early holocene wind strength in the mid latitudes of the southern hemisphere from aeolian dust in the tasman sea dust transported by southern hemisphere mid latitude westerly winds from australia and deposited in the tasman sea shows no evidence for stronger winds during the last glacial maximum lgm compared to the holocene features of the particle size distributions of the dust do however indicate enhanced dry deposition of dust in the lgm changing to rainfall scavenging during deglaciation and the early holocene as climate ameliorated from these results it appears that activation of desert dunefields over 40 of australia during the lgm was the result of a reduction in stabilizing vegetation and more frequent episodes of sand movement rather than of increased wind strength the lgm climate of inland australia must have been considerably more stressful for plants as a result of lower precipitation and or carbon dioxide stress to achieve the implied levels of surface destabilization enhanced atmospheric dust loads in the southern hemisphere and deposition over antarctica were most likely the result of greatly expanded source areas in the mid latitude southern continents and a weaker hydrological cycle rather than greater entrainment or more efficient transport by stronger winds during the lgm wind strength appears to have varied regionally and predominantly in high latitudes rather than uniformly for all zonal winds

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

revisiting the chronology and environmental conditions for the accretion of late pleistocene early holocene pampean loess argentina abstract the present research work reviews the age models of three previously studied loess sections across 700 km in the loess belt of the pampean region in central argentina the loess sections were investigated for the first time through high resolution luminescence dating in order to determine the chronology of the loess deposits and its temporal correlation with important palaeoclimatic records of the southern hemisphere reliable estimations of mass accumulation rates mars for loess were used to infer the temporal dust flux variation during the last glacial interglacial transition in southern south america the new age models have significant differences compared to the previously published ones of likely last glacial maximum lgm ages the three studied sections showed general bimodal grain size distributions consistent with multiple sources contributing dust to the pampas it is observed that higher mars values are associated with an increased presence of finer loess increases in loess accumulation are coeval with climatic transitions from wetter to drier periods in the puna altiplano plateau and high mars are related to synchronous climatic shifts to humid conditions in the pampean plain contrasting with dust fluxes observed in the more distal palaeoarchives i e the south atlantic ocean and the antarctic ice sheet the new data suggest increased dust accumulation in the pampas during the antarctic cold reversal acr and the holocene this supports the idea that changes related to atmospheric transport efficiency can better explain dust flux variations observed over glacial interglacial periods in distant palaeoarchives

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

high latitude dust deposition in snow on the glaciers of james ross island antarctica high latitude dust hld depositions on four glaciers of james ross island the ulu peninsula were analysed the deposition rate on the selected glaciers varies from 11 8 to 64 0 g m 2 which is one order of magnitude higher compared to the glaciers in antarctica or elsewhere in the world a strong negative relationship between the sediment amount and altitude of a sampling site was found this is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer general southerly and south westerly wind directions over the ulu peninsula with exceptions based on local terrain configuration help to explain the significantly lower level of sediment deposition on san jose glacier and the high level on triangular glacier x ray fluorescence xrf spectrophotometry was used to estimate the relative proportions of the main and trace lithophile elements in the sediment samples both the sediment amount and the xrf results are analysed in a depth profile at each locality and compared among the glaciers suggesting long range transport of fine mineral material from outside james ross island the distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the ulu peninsula

mid latitude trans pacific reconstructions and comparisons of coupled glacial interglacial climate cycles based on soil stratigraphy of cover beds abstract south westland new zealand and southern chile are two narrow continental corridors effectively confined between the pacific ocean in the west and high mountain ranges in the east which impart significant influence over regional climate vegetation and soils in both these southern mid latitude regions evidence for extensive and repeated glaciations during cold phases of the quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants in south westland these variably aged glacial landforms are mantled by layered multisequal soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment these cover bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial warm and glacial cold climate during the quaternary in this study we recognise multisequal soils overlying glacial landforms in southern continental chile but unlike the spodic podzolic soil sequences of south westland these are of dominantly volcanigenic andic provenance and are very similar to multisequal soils of andic provenance that predominate in and adjacent to areas of rhyolitic to andesitic volcanism in north island new zealand here we develop a soil stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental chile based on proxy data from southern chile we propose that persistent vegetation cover and high precipitation on the western side of the andes during colder than present episodes tended to suppress the widespread production of glacially derived loessial materials despite the pervasive occurrence of glacial and glacio fluvial deposits that have frequently inundated large tracts of this landscape during the quaternary given the lack of loess cover beds that have traditionally assisted in the relative dating of glacial episodes prior to the late quaternary surface exposure dating techniques could provide another chronological alternative to address this issue however there have been two main obstacles to successfully apply this dating technique in patagonia first minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion although dating outwash plains is more robust second on the wet western side adjacent to the andes persistent vegetation cover during both glacial and post glacial times as well as widespread inundation by volcanic mass flows appear preventive we make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted andean sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified as already demonstrated by new zealand studies multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the quaternary on this basis similar sequences in northwest patagonia provide a relatively untapped archive to enable quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed

loess soil stratigraphy and aokautere ash on late pleistocene surfaces in south westland new zealand interpretation and correlation with the glacial stratigraphy the detailed stratigraphy and chronology for late pleistocene glaciations in north westland have not previously been applied to glacial deposits and landforms of south westland in part because of lack of exposure a stratigraphy for loess coverbeds offers the potential for discriminating and correlating landforms in this region this study in saltwater forest and surrounding areas in south westland confirms the presence of loess and of the incorporated 22 600 bp radiocarbon years aokautere ash beneath late pleistocene moraine and terrace surfaces loess sheets are thin ca 40 cm thick and accretion rates have been low ca 30 mm ka 1 during the last stadial of the last glaciation boundaries between loess sheets were placed at the surface of buried soils paleosols identified from their morphology criteria for recognition of buried soils differ between the moderately well drained moraine sites and poorly to extremely poorly drained terrace sites five loess sheets have been recognised and correlated to the oxygen isotope record on the basis of the position of maximum counts of glass shards of aokautere ash pollen analysis and radiocarbon dates loess sheets 1 and 2 are of last otira glacial age loess sheet 3 accumulated during the last kaihinu interglacial and loess sheet 4 accumulated during the penultimate waimea glaciation loess sheet 5 is of at least waimean age

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

dust accumulation in the new zealand region since the last glacial maximum abstract loess is widespread in new zealand deposits 1 m thick cover 10 of the land area it has mainly been derived from dust deflated from river floodplains during the last glacial maximum lgm dust accumulation continues today downwind of major river floodplains most loess is quartzofeldspathic having its origins in mesozoic and neogene rocks of the axial ranges and hill country in the central north island there are deposits of volcanic loess derived from aeolian reworking of tephras loess morphology and properties vary greatly due to diverse parent materials post depositional climates and drainage conditions the widespread 26 170 cal yr kawakawa tephra provides a datum for calculating mass accumulation rates mars rates are mostly within the range 70 150 g m 2 yr 1 but enhanced deposition at one site gave a rate of 360 g m 2 yr 1 contemporary mars of 40 100 g m 2 yr 1 were determined for distances of 1 75 0 4 km downwind of the rakaia river lgm mars of quartz for two marine cores p69 q858 drilled 100 300 km east of new zealand are 40 70 g m 2 yr 1 the mar of the aeolian component of p69 is estimated to be ca 15 g m 2 yr 1

meteorological controls on wind erosion during foehn wind events in the eastern southern alps new zealand foehn winds in the lee of mountain barriers create highly favourable meteorological conditions for wind erosion in alpine areas and over adjacent lowlands this paper presents meteorological observations made during winter and summer foehn wind erosion events as part of a 3 year investigation into the physical nature and incidence of eolian processes in the eastern southern alps new zealand foehn winds were observed to initiate eolian activity including dust storm genesis when mean near surface wind speeds exceeded 7 8 m s 1 over a 20 min period in the absence of precipitation wind speeds of 25 30 m s 1 were frequently recorded during typical foehn events and wind speed maxima of 40 50 m s 1 were monitored during severe foehn windstorms saltation clouds sampled at 0 5 and 1 m above glaciofluvial deposits during foehn wind erosion events were found to display a mean grain size of between 300 and 435 m the entrainment of fine grained surface sediments by the airstream appeared to be enhanced in late autumn may and early spring september by freeze thaw cycles that were observed to result in needle ice growth in exposed glaciofluvial and lacustrine deposits the needle ice fragmented such deposits producing surfaces that were aerodynamically rough and highly susceptible to deflation by the airstream following a thaw observations made by this study are thought to be similar to foehn wind erosion events reported in the lee of other substantial mountain ranges such as the rocky mountains andes hindu kush and karakoram

bending of the bolivian orocline and growth of the central andean plateau paleomagnetic and structural constraints from the eastern cordillera 22 24 s nw argentina 1 we report new paleomagnetic and structural data from late cretaceous to mio pliocene continental sandy silty sedimentary rocks from the eastern cordillera central andes here n s to nne ssw ridges hosting paleozoic basement and upper cretaceous continental red beds overthrust thick adjacent cenozoic basins pretilting and likely primary reliable directions gathered at 15 sites document 45 9 9 4 30 1 23 9 and 15 4 19 3 clockwise cw rotations with respect to south america occurring after the late cretaceous 80 ma oligo miocene 20 30 ma and late miocene pliocene 5 10 ma respectively conversely four upper cretaceous sites from the walls of a n s left lateral strike slip fault yavi abra pampa fault yield a null rotation about 20 km to the west flower structures and subvertical syntectonic strata dated at 14 26 0 19 ma are exposed along the subparallel abra moreta left lateral strike slip fault relying on data from the literature on the period when deformation began we suggest that since eo oligocene times 30 40 ma the eastern cordillera has undergone a regional cw rotation of 40 50 synchronous with crustal shortening and large scale bending of the andean salient the cw rotation is possibly still active today as documented by regional gps data from the andes since 15 ma ago the activity of n s left lateral strike slip faults induced counterclockwise rotations along the fault zone locally annulling the regional cw rotation in agreement with a previous model we speculate that mid miocene strike slip activity accommodated the progressive southward spreading of the altiplano puna high altitude plateau laterally migrating from the overthickened crustal region of the salient apex

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

pedogenesis by upbuilding in an extreme leaching and weathering environment and slow loess accretion south westland new zealand abstract soil formation is usually envisaged as acting from the surface downwards in many environments however the accumulation of sediment and soil formation are contemporaneous it is only where the rate of one process far exceeds the rate of the other that assumptions of topdown pedogenesis are appropriate the aspect of upbuilding pedogenesis that distinguishes it from topdown pedogenesis is that each increment of soil below the a horizon has experienced processes characteristic of all horizons above it this study examines the influence of upbuilding soil formation in a high rainfall environment of rapid soil formation and slow loess accretion an environment where upbuilding could have a noticeable influence on soil properties soils formed by topdown soil formation topdown soils are compared with soils formed in loess that accumulated from early last glaciation to the holocene upbuilding soils soils are compared in two environments alaquods on poorly drained terraces and placorthods or dystrochrepts on well drained moraine crests we have assumed that properties of the upbuilding soils inherited during the current topdown phase of pedogenesis beginning in the holocene are analogous to those in the topdown soils in this manner soil properties evolved during upbuilding are distinguished in well drained upbuilding soils on moraines subsoil organic carbon has mineralised so that profile trends are very similar to corresponding topdown soils upbuilding has enhanced weathering in subsoils which is reflected in lower ph lower total p and lower primary inorganic p than in topdown soil counterparts total p concentrations in upbuilding soils are much lower than unweathered loess and constant throughout the subsoil and there is almost no p in primary forms in contrast total p in c horizons of topdown soils reaches concentrations typical of the parent material and more than 30 of this is in a primary inorganic form the differences are attributed to each subsoil increment of upbuilding soils having been part of acid a and e horizons oxalate extractable fe and al data indicate that podzolisation was active during upbuilding poorly drained upbuilding soils on terraces have higher subsoil organic carbon inherited from former a or o horizons than comparable topdown soils buried a and o horizons inherited during upbuilding and preserved in the reducing conditions have acted as sinks for mobile al and now resemble podzolic illuvial bh horizons upbuilding through addition of loess to soils promotes a pedogenic pathway distinct from topdown pedogenesis consequently soil chronosequence studies that include soils on old loess mantled surfaces do not strictly satisfy the assumptions of soil chronosequences the nature and rate of soil processes inferred from these studies need revisiting the findings of this study are transferable to other environments where the rate of soil formation and sediment accumulation are comparable

late glacial and early holocene glacier activity in the southern alps new zealand abstract in the southern alps of new zealand glaciers advanced to their last glacial maximum limits between 22 3 and 18 ka bp and there is evidence for at least four more advances between 18 and 8 ka bp a widespread glacier advance possibly with two maxima occurred between 16 and 14 ka bp during which glaciers reached positions close to those attained at the last glacial maximum after 14 ka bp there was a significant and sustained retreat of glaciers that marks the beginning of the post glacial interval in new zealand locally known as the aranui interglacial during the aranui there is evidence for a much smaller glacier advance around 11 ka bp that may have been coeval with the younger dryas stade but opinions on this are still controversial two younger ice advances may have occurred close to 10 25 and 8 6 ka bp although regional patterns of late glacial advances are reasonably well established the post glacial advances are known only from single sites and require closer investigation

dust deposits on la graciosa island canary islands spain texture mineralogy and a case study of recent dust plume transport abstract la graciosa volcanic island evolved in the late pleistocene holocene it is situated along the northeast of the canarian archipelago with a subaerial surface of 27 km2 this island is located close to the western sahara being 80 km from the north western african continental shelf and 145 km from the coast the island supports a very small permanent population the climate is coastal arid 116 mm precipitation per annum regular occurrences of saharan dust plumes about 30 of the year with a dust accumulation rate of 20 g 2 year 1 produce sedimentation of dust on the island of ca 540 t year 1 wind blown sediments cover a large area more than 52 of the otherwise volcanic island forming sandy beaches sand sheets nebkhas and other aeolian deposits re distributed dust deposits often occur on the leeward sides of inter volcano areas inter dune areas and in endorheic sediment traps many of these deposits are edaphized and carbonatized textural analysis of the dust deposit samples shows a variable proportion of silt 80 20 clay 19 9 and fine to very fine sand 71 4 the general mineralogical composition of these sediments as measured by xrd and sem eds is calcite 26 illite 26 quartz 11 augite 10 aragonite 6 anorthite 8 kaolinite 5 and montmorillonite 3 the mineralogy in different size fractions is very consistent for example quartz content decreases from 15 in the coarse silt fraction to 5 in the fine sand a mineral and grain size comparison with airborne dust collected on gran canaria island was undertaken close similarities were found in the two sample sets such closely matched characteristics point to a similar origin for both airborne dust and dust deposits in line with the saharan plume dust that regularly traverses this archipelago it is unusual to find so much quartz in the fine sand fraction of these aeolian dust deposits individual quartz grains with an intermediate axial length of 160 m were identified by sem eds previous investigators have found similar giant particles in long range transported aeolian dust middleton et al 2001 in contrast to the classic model for gravity settling of airborne dust particles the debate on this subject remains open for discussion we present evidence of long range wind transported large mineral particles and a 2004 case study of uplift wind velocity vs plume dust generation as well as a transport efficiency model that can explain the existence of fine sand in the dust deposits on la graciosa island and in the airborne samplers on gran canaria island recent saharan dust shows that about 10 of similar coarse grained particulate matter is also present

the contorted new england orogen eastern australia new evidence from u pb geochronology of early permian granitoids 1 a series of sharp bends oroclines are recognized in the paleozoic to early mesozoic new england orogen of eastern australia the exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated here we present zircon u pb ages that confirm the lateral continuation of early permian 296 288 ma granitoids and shed new light on the oroclinal structure orogenic curvature is defined by the alignment of early permian granitoids parallel to the structural grain of the orogen as well as the curved geometry of sub vertical deformation fabrics forearc basin terranes and serpentinite outcrops alternative geometrical interpretations may involve two bends texas and coffs harbour oroclines three bends manning orocline or even four bends nambucca orocline we argue that the model involving four bends is most consistent with available data although further kinematic constraints are required to confirm the existence of the manning and nambucca oroclines a subsequent phase of younger magmatism 260 ma cuts across the curved structural grain providing a minimum age constraint for orocline development assuming a structure of four oroclines we suggest a tentative tectonic model that involves an early stage of subduction curvature during slab rollback at 300 285 ma followed by bending associated with dextral transpression a final tightening of the curved structures was possibly obtained by e w shortening during the late permian to triassic 265 230 ma hunter bowen orogeny

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

aeolian dust transport and deposition by foehn winds in an alpine environment lake tekapo new zealand abstract observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes including dust storm genesis a mean wind speed during foehn windstorms of 7 5 m s 1 at 2 65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin particularly from the dry braid channels of glacier fed rivers exposed lacustrine deltas and degraded tussock grasslands this threshold entrainment velocity is similar to others presented within the international literature for such surface types a diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes such as dust entrainment are most likely to occur from late morning to early evening however where topography enhances wind speeds for example by channelling airflow down river valleys favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation potential dust roses were determined for two sites within the lake basin the dust roses supported anecdotal and observational evidence of principle dust sources within the study area and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust once the physical trigger conditions for dust entrainment are known this requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates especially in complex terrain where many micro climates often exist

morphostructure at the junction between the beata ridge and the greater antilles island arc offshore hispaniola southern slope abstract oblique convergence between the caribbean plate s interior and the inactive greater antilles island arc has resulted in the collision and impingement of the thickened crust of the beata ridge into southern hispaniola island deformation resulting from this convergence changes from a low angle southward verging thrust south of eastern hispaniola to collision and uplift in south central hispaniola and to left lateral transpression along the southern peninsula of haiti in western hispaniola using new swath bathymetry and a dense seismic reflection grid we mapped the morphological structural and sedimentological elements of offshore southern hispaniola we have identified four morphotectonic provinces the dominican sub basin the muertos margin the beata ridge and the haiti sub basin the lower slope of the muertos margin is occupied by the active muertos thrust belt which includes several active out of sequence thrust faults that were they to rupture along their entire length could generate large magnitude earthquakes the interaction of the thrust belt with the beata ridge yields a huge recess and the imbricate system disappears the upper slope of the muertos margin shows thick slope deposits where the extensional tectonics and slumping processes predominate the northern beata ridge consists of an asymmetrically uplifted and faulted block of oceanic crust our results suggest that the shallower structure and morphology of the northern beata ridge can be mainly explained by a mechanism of extensional unloading from the upper cretaceous onward that is still active residually along the summit of the ridge the tectonic models for the northern beata ridge involving active reverse strike slip faults and transpression caused by the oblique convergence between the beata ridge and the island arc are not supported by the structural interpretation the eastern bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharp along strike transition from low angle thrusting to collision and uplifting

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

diachronous post orogenic magmatism within a developing orocline in iberia european variscides 1 u pb zircon crystallization ages of 52 late variscan granitoid intrusions from nw iberia 19 from new data 33 from previous studies constrain the lithospheric evolution of this realm of the variscan belt of western europe and allow assessment of the relationship between oroclinal development and magmatism in late carboniferous early permian times the u pb ages in conjunction with a range of geological observations are consistent with the following sequence of events i oroclinal bending starts at 310 305 ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts ii between 305 and 300 ma melting continues under the outer arc of the orocline central iberian zone of the iberian variscan belt and mid crustal melting is initiated coevally the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure iii between 300 and 292 ma foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle iv cooling of the lithosphere between 292 and 286 ma resulting in a drastic attenuation of lower crustal high temperature melting by 285 ma the thermal engine generated by orocline driven lithospheric thinning delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts the model proposed explains the genesis of voluminous amounts of granitoid magmas in post orogenic conditions and suggests that oroclines and similar post orogenic granitoids common constituents of numerous orogenic belts may be similarly related elsewhere

marine magnetic signature of the last glacial maximum and last deglaciation from the southern hemisphere mid latitudes abstract an environmental magnetic record is presented from piston core tan0712 23 collected on the southern flank of challenger plateau at a water depth of 2817 m magnetic grain size and concentration variations during the last glacial maximum lgm are interpreted to reflect variations in terrestrial influx corresponding to glacial advance and stagnation events on millennial time scales the lgm signal between 25 and 23 ka demonstrates an antiphase relationship with northern hemisphere records implying that the bipolar seesaw was active during that period the number and timing of features in tan0712 23 suggest that lgm millennial scale climate fluctuations are strongly realized in the mid latitudes possibly due to amplification by regional forcing mechanisms the onset of the deglacial magnetic signal defined by a low concentration of magnetic minerals is constrained at 18 6 cal ka bp by the radiocarbon age model and corresponds to southward migration of the southern hemisphere westerly wind system and subtropical front

a detailed 31 000 year record of climate and vegetation change from the isotope geochemistry of two new zealand speleothems abstract uranium series dating and stable isotope analyses of two speleothems from northwest nelson new zealand record changes in regional climate and local forest extent over the past 31 000 years oxygen isotope variation in these speleothems primarily represents changes in the meteoric waters falling above the caves possibly responding to latitudinal changes in the position of the subtropical front in the tasman sea seven positive excursions can be identified in the oxygen isotope record which coincide with periods of glacier advance known to be sensitive to northward movement of the subtropical front four glacier advances occurred during oxygen isotope stage 2 with the most extreme glacial conditions centered on 19 000 cal yr b p 2 an excursion in the oxygen isotope record from 13 800 to 11 700 cal yr b p provides support for a previously identified new zealand glacier advance at the time of the younger dryas stade but suggests it began slightly before the younger dryas as recorded in greenland ice cores carbon isotope variations in the speleothems record changes in forest productivity closely matching existing paleovegetation records on the basis of vegetation changes stage 2 glacial climate conditions terminated abruptly in central new zealand from 15 700 to 14 200 cal yr b p evidence of continuous speleothem growth at one site suggests that depression of the local treeline was limited to 600 700 m below its present altitude throughout the last 31 000 years

dust transportation and deposition in a superhumid environment west coast south island new zealand contemporary rates of dust deposition monitored along a 300 km section of the superhumid west coast of new zealand s south island are presented in this setting dust is entrained primarily from the dry channels of braided glaciofluvial rivers that drain the western slopes of the southern alps measured dust deposition ranged between 0 21 and 118 9 kg 1 ha 1 month 1 which is similar to dust deposition rates monitored in arid and semiarid environments however these are not considered to be sufficient for present day loess genesis dust deposition was highest in summer because of the greater frequency of favourable dust transporting winds and the effect of rainfall was secondary dust transportation occurred mainly during the passage of nonprecipitating cold fronts or postfrontal southwesterlies transportation also occurred during prefrontal conditions and in winter fohn southeasterlies were the predominant dust transporting winds to affect the west coast

rates and environmental controls of aeolian dust accumulation athabasca river valley canadian rocky mountains abstract despite an abundance of sedimentary archives of mineral dust i e loess accumulations from cold humid environments the absence of contemporary process investigations limits paleoenvironmental interpretations in these settings dust accumulations measured at jasper lake a seasonally filled reach of the glacially fed athabasca river in the canadian rocky mountains are some of the highest contemporary rates recorded to date high deposition rates including a maximum of 27 632 kg ha 1 month 1 occur during river low flow periods but even the lowest deposition rates occurring during bankfull periods exceed other contemporary rates of deposition high rates of dust deposition may be attributed to geomorphic and climatic controls affecting sediment supply availability and transport and biologic factors affecting accumulation localized confinement of the jasper river by tributary river alluvial fans has caused channel expansion upstream and formation of the shallow depositional basin known as jasper lake this localized sedimentary basin coupled with large seasonal water level fluctuations and suitably high wind speeds favors seasonal dust production in addition a dense source proximal coniferous forest stand encourages high dust accumulation via increased aerodynamic roughness and airflow deceleration the forest stand also appears to act as an efficient dust filter with the interception and storage of dust by the forest canopy playing a significant role with regards to secondary fallout and sediment accumulation overall these results provide new insights on the environmental controls of dust entrainment and accumulation in cold humid settings and help clarify controls on the formation of holocene river sourced loess deposits

aeolian dust transport and deposition over crete and adjacent parts of the mediterranean sea monitoring of dust deposition at several stations on crete over a three year period has shown that the present day depositional flux is of the order of 10 100 gm 2 yr 1 most of the dust deposition takes place during a few annual dust events which typically last for 1 3 days dust haze episodes are usually associated with southerly or southwesterly winds which transport fine sediment from north africa dust is raised by a wide variety of meteorological conditions which generate strong near surface winds in the source areas but major long range transport events are often associated with cold fronts linked to the passage of deep mid latitude depressions during winter and spring dust haze frequency and deposition rates are highest in western crete and decrease towards the east suggesting that transport from tunisia and neighbouring parts of north africa is particularly important the measured rate of dust deposition is well below the minimum level required for loess formation deposits which have previously been identified as loess are shown to be uncemented marine marls of tertiary age laboratory analysis of red soils surface sediments and bedrock samples has confirmed that many of the soils contain an important aeolian dust component but it is concluded that a more important source of soil parent material is provided by weathering of local rocks many of the soils contain significant amounts of quartz sand which cannot have been transported across the sea from north africa reworking of weathered material and deposited dust is extensive and is accomplished by both aeolian and fluvial processes tectonically controlled depressions in the mountains and parts of the coastal lowlands have acted as long term sinks in which a thickness of several metres of sediment and soil has accumulated during the quaternary

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

upbuilding pedogenesis under active loess deposition in a super humid temperate climate quantification of deposition rates soil chemistry and pedogenic thresholds abstract although the importance of dust deposition as an integral component of terrestrial biogeochemical cycles is well recognised few studies have directly addressed pedogenic processes associated with dust deposition on the land surface itself and if so mainly as relict features this work addresses this gap by looking at the pedogenic response to an active loess flux gradient in a super humid strong weathering environment on the west coast of new zealand s south island along the gradient seven soil pits were examined for a range of soil physical colour texture bulk density structure roots and chemical properties ph fe o fe d al o soil organic carbon measured to a depth of 50 cm to capture the transitional changes arising from minimal to maximal loess deposition rates maximal deposition rate was estimated to be 28 4 g m 2 y 1 along the gradient towards the highest deposition rate loess free sandy spodosols changed to increasingly more finely textured soils ultimately featuring a two fold increase of silt the pedogenic oxides fe o fe d and al o gradually increased each by 50 and soil organic carbon by 60 these increases were facilitated by continuous accession of loess the loess mixed with organic matter at the surface and became increasingly weathered and leached with the time that it had spent undergoing eluviation subsequently the loess increments were buried within the subsoil as part of an upwardly thickening spodic horizon upbuilding pedogenesis because of the high deposition rates under maximum loess flux spodosol formation became ultimately retarded and an inceptisol formed because loess supply overwhelmed topsoil leaching having also an illuvial subsoil horizon this inceptisol showed the strongest chemical indicators for podzolisation of the gradient soil data from supplementary sites suggested that more developed soils required lower loess fluxes to retard further pedogenic differentiation than younger soils the existence of a loess gradient that is capable of forming distinctive deposits in a super humid environment gives evidence that not only dry arid climates e g during glacials are potentially suitable for the formation of aeolian substrates loess the study indicates enhanced soil organic carbon storage in soils as a result of loess deposition and concomitant pedogenesis

aeolian transport of sediment on a beach during and after rainfall wildwood nj usa abstract a field investigation was conducted 9 march 1994 on a dissipative beach to compare wind characteristics and aeolian transport during and after a light rain winds blew alongshore during the monitoring period moisture content of surface sediment on the backbeach was above 7 during rain and 4 four hours after rainfall ceased trapping rates measured using a cylindrical vertical trap were 14 1 kg m 1 h 1 during rainfall and 140 2 kg m 1 h 1 for a period beginning 3 h 33 min after rainfall ceased results indicate that light rain resulting in bulk surface moisture values over 7 is not sufficient to eliminate transport but the rate of transport is lower than can occur on the beach three to four hours following rain the amount of sand trapped at wildwood during rainfall is relatively high when compared to many previous studies on beaches in the absence of rain the great length of the beach as a source area combined with parallel or oblique winds are significant in increasing rates of sediment transport

dating of lithospheric buckling 40ar 39ar ages of syn orocline strike slip shear zones in northwestern iberia abstract orogenic curvature is a ubiquitous feature of mountain belts and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate in order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development however determining the absolute isotopic timing of oroclinal bending is challenging the most direct method available to constrain the time interval during which an orocline formed is to obtain absolute age constraints on fabrics generated within syn orocline strike slip shear zones that accommodated rotations around a vertical axis during the development of crustal or lithospheric scale orogenic curvature here we present a data set of 40ar 39ar ages obtained from five shear zones some of which display curved traces parallel to the cantabrian orocline structural grain in nw iberia and are interpreted to have been generated coevally to it the 40ar 39ar ages were obtained by laser rastering induced step heating on single muscovite crystals that grew synkinematically during shearing all five samples yielded ages that cluster tightly at 308 3 ma providing direct evidence for the age of oroclinal bending this age is consistent with the age constraints obtained from paleomagnetic and structural data that place the onset of oroclinal bending in moscovian times our 40ar 39ar age determinations therefore provide a reliable absolute constraint on the age of buckling of the variscan orogen around a vertical axis and provide further evidence that oroclinal bending is unrelated to variscan convergence collision or the subsequent extensional collapse of the mountain belt

thermoluminescence ages of post glacial loess rakaia river south island new zealand abstract we applied the partial bleach r beta thermoluminescence tl dating technique to two samples from massive post glacial loess overlying the last major aggradation gravel burnham formation near barrhill on the south bank of the rakaia river this site is roughly midway between the coast and the front range of canterbury previously the time of initiation of deposition of such loess in the region was only poorly constrained to somewhere between the interval 16 32 ka and ca 11 ka loess deposition has continued until today along margins of major braided rivers sample bhl 5 30 cm above the gravel gave a tl age of 11 7 1 9 1 ka and sample bhl 1 1 35 m above bhl 5 and 1 9 m below the surface gave an age of 5 49 0 70 ka thus age depth extrapolation at the barrhill site implies that loess deposition began at 13 2 ka and continued through the holocene to the present the average rate of deposition between the two tl samples was 0 22 0 07 mm year analytical error only and possibly greater thereafter the presence of the loess wedge dating from 13 2 ka indicates that the rakaia river began to entrench at about this time in this middle segment of the piedmont plain

the last glacial interglacial transition lgit in south westland new zealand paleoecological insight into mid latitude southern hemisphere climate change abstract high resolution pollen stratigraphy from three peat cores located within 20 km of lateglacial moraines in south westland new zealand provide detailed records of climate change during the last glacial interglacial transition lgit the pollen record shows the replacement of grassland by shrubland prior to ca 15 300 14 c yr bp 18 300 cal yr bp followed by the progressive development of broadleaf shrubland and scattered forest prior to ca 12 000 14 c yr bp 14 400 cal yr bp local vegetation changes around the time of the younger dryas chronozone 11 10 ka 14 c bp are evident but are not necessarily a result of regional climate cooling vegetation changes between ca 12 000 and 10 000 14 c yr bp 14 400 and 11 400 cal yr bp indicate a period of increased precipitation tall podocarp forest similar to that of the contemporary forest was well established by ca 10 000 14 c yr bp 11 400 cal yr bp a period of increased westerly circulation over southern new zealand is considered to be the most likely mechanism for causing the increased precipitation between ca 12 000 and 10 000 14 c yr bp 14 300 and 11 400 cal yr bp increased precipitation would also provide a mechanism for initiating lgit ice advance in the area data from these records show some support for global climate change models that propose inter hemispheric linkage but may be more supportive of a climate change model that incorporates an increased westerly circulation over southern new zealand during the lgit