mid and late holocene fluvial dynamics in the tropical guapi macacu catchment southeast brazil the role of climate change and human impact abstract deeply incised middle to late holocene fluvial sediments of several streams in the tropical guapi macacu river catchment in the state of rio de janeiro were investigated with stratigraphical sedimentological and geochronological methods these investigations revealed multiple changes of the fluvial dynamics during the holocene triggered by a millennial climate change and the post colonial increase of land use reduced fluvial dynamics and geomorphic stability prevailed in this region during the relatively dry mid holocene from 6 6 until 4 7 cal ka bp this phase of stability was followed by a period of geomorphic activity as indicated by increased fluvial dynamics from this date this overall environmental change corresponds well with the onset of quasi modern humid climate conditions in southeastern brazil during the mid to late holocene transition a new period of activity has taken place since 0 29 cal ka bp in relation with the start of european colonization and increased land use pressure large areas of atlantic forests were converted into agricultural and pasture land causing strong soil erosion and destabilized slopes the results of these investigations improve the existing holocene landscape evolution model and highlight that under the given specific climatic and environmental conditions even a closed forest cover does not necessarily result in geomorphic stability

structural evolution of the texas orocline eastern australia the texas orocline with a half wavelength of similar to 120 km is the largest and most obvious orocline in the southern new england orogen and is clearly recognised in geological maps and geophysical images in the area of the orocline there is a major unconformity between devonian carboniferous metasedimentary rocks texas beds and the overlying early permian rift related basins detailed structural mapping shows that units both above and below the unconformity are folded around the orocline indicating that at least part of the oroclinal deformation has occurred after the deposition of the early permian rocks in addition early permian 298290 ma granitoids are aligned parallel to the oroclinal structure further indicating that deformation partly occurred during or after the early permian pre oroclinal isoclinal folds f 1 and related axial plane cleavage si are well developed in the texas beds and are curved around the oroclinal structure syn oroclinal structures are characterised by minor kink folds and disharmonic folding f 2 in the core of the orocline a later phase of kink folding corresponding to a similar to n s shortening direction does not seem to be related to the orocline and is interpreted as post oroclinal deformation a secondary penetrative fabric parallel to the axial plane of the orocline was not observed indicating low contractional shortening across the orocline 30 we demonstrate that the observed strain is too low to account for oroclinal bending during dextral transpression as previously proposed we suggest an alternative model involving an initial curved structure probably related to subduction rollback or a pre existing curvature in the palaeomargin of eastern australia which was amplified by dextral transpression and subsequent e w contraction c 2011 international association for gondwana research published by elsevier b v all rights reserved

spatial variability of soil properties at different scales within three terraces of the henares river spain abstract this paper applies statistical and geostatistical procedures to a soil chronosequence on the terraces of the henares river ne madrid to analyse the spatial distribution of several soil properties and use the contribution of geostatistics to establishing a landscape evolution model of the area particle size distribution ph calcium carbonate and organic carbon were analysed statistical procedures focus on analysing differences between terraces geostatistical procedures identify short and medium range variations within individual terraces at different scales standard transitive variogram models describe the properties of the younger terrace whereas the linear intransitive model fits the majority of variograms of the older terrace the analysis confirms and quantifies the decrease in variability of soil properties from young to old deposits showing thus an increment of soil homogenisation with time ageing of the terraces causes the variables to show nontransitive variogram models with unbounded variances within the observation range

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

the hydrological and environmental evolution of shallow lake melincue central argentinean pampas during the last millennium summary lake melincue located in the central pampean plains of argentina is a shallow 4 m subsaline lake tds 2000 ppm highly sensitive to hydrological changes the modern shallow lake system is composed of a a supralittoral area which includes a narrow mudflat a vegetated mudflat and wetlands subenvironments and b the main water body comprising lacustrine marginal and inner areas the development and extension of these subenvironments are strongly conditioned upon lake surface fluctuations past environmental changes were reconstructed through sedimentological physical and geochemical proxy analyses of two short sedimentary cores 127 cm well constrained 210 pb ages profiles were modeled and radiocarbon chronologies were determined covering a period from ad 800 to the present the analyzed sedimentary cores from lake melincue allowed for the reconstruction of past hydrological scenarios and associated environmental variability ranging from extremely low lake levels during dry phases to pronounced highstands at wet periods the paleohydrological reconstruction revealed very shallow conditions in the period between ad 806 and ad 1880 which was registered by massive deposits with low organic matter relatively wetter phases disrupting this dry period were represented by organic matter increases a major wet phase was registered by ad 1454 after the end of the medieval climate anomaly a subsequent abrupt shift from this wet phase to drier conditions could be matching the transition between the end of the medieval climatic anomaly and the beginning of the little ice age the occurrence of sedimentary hiatuses between ad 1492 and ad 1880 in melincue sequence could correspond to intensive droughts during the little ice age after ad 1880 banded and laminated autochthonous organic matter rich sediments registered an important lacustrine transgression and the onset of a permanent shallow lake corresponding to the beginning of the current warm period the uppermost recent fine grained low salinity organic sediments represent a lake transgression occurred in the 1970s coeval with a general increase in precipitation across southeastern south america this transgression is registered regionally in other pampean lakes and in the 20th century instrumental records of lake melincue this paleoenvironmental reconstruction provides a new high resolution record that registers striking hydroclimatic changes occurred at a regional scale across the pampean plains during the last millennium and it contributes to understand the past climatic history in southeastern south america

early to middle holocene transition in the pastos chicos record dry puna of argentina abstract this paper presents a multi proxy record and its paleoenvironmental interpretation from pastos chicos 23 40 29 s 66 25 32 w 3781 m asl susques jujuy province argentina the analysis includes a study of fluvial sediments and geomorphology and the contained diatoms and pollen record at centenary resolution two main environmental phases characterize the 9000 4200 bp interval the first phase was a humid period between 9000 and 7300 bp circa 10 000 8100 cal bp which showed organic soils formation in a floodplain broadly vegetated by grasses with a high and stable water table level the second phase developed between 7300 and 6000 bp 8100 6800 cal bp and showed a moderately drier environment interrupted by punctuated humid events such as those around 7000 and 6300 bp this environment could be interpreted as a permanently existing meandering river with a floodplain with shallow oxbow lakes bordered by a diverse shrub steppe after 6000 bp the fluvial system turned into a braided river situated in a sandy floodplain with dunes and ephemeral ponds at the end of the sequence i e post 4200 bp salt crusts developed and the river lowered its base level by 8 m these results seem to show that the pastos chicos river basin evolved from low energy and more humid conditions established during the early and the first part of the middle holocene to drier ones in a system with more energy during some events of the second part of the latter period the start of this aridization process at 6000 bp in the basin seems to be substantially later than other observations in local records of the andean area this could be due to physiographic control of the moisture by the catchment area 1000 km2 that generates a catchment averaged regional scale signal of smaller amplitude which is delayed for individual tributaries these studies with other ongoing analysis will improve the accuracy of the models of resource structure in the area in several space time scales and consequently advance knowledge concerning the organizational pattern of human societies in the past

timing and structure of mega sacz events during heinrich stadial 1 a substantial strengthening of the south american monsoon system sams during heinrich stadials hs points toward decreased cross equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales in order to better constrain the exact timing and internal structure of hs1 over tropical south america we assessed two precisely dated speleothem records from central eastern and northeastern brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial atlantic during hs1 we recognize at least two events of widespread intensification of the sams across the entire region influenced by the south atlantic convergence zone sacz at 16 11 14 69 kyr b p and 18 1 16 66 kyr b p labeled as hs1a and hs1c respectively separated by a dry excursion from 16 66 to 16 11 kyr b p hs1b in view of the spatial structure of precipitation anomalies the widespread increase of monsoon precipitation over the sacz domain was termed mega sacz

holocene vegetation changes along the southeastern coast of the argentinean pampa grasslands in relation to sea level fluctuations and climatic variability palynological analysis of alluvial sequences from arroyo claromeco abstract here we present palynological records from alluvial deposits in four outcrop sequences along the lower reaches of arroyo claromeco buenos aires province argentina 38 50 s latitude 60 05 w longitude these data indicate development of soils and grasslands with associated halophytic vegetation in the higher elevations of the floodplains between ca 7200 and 6000 14 c yr bp ca 8000 and 7000 cal yr bp at lower elevations halophytic saltmarsh vegetation was replaced by wetland communities sedges in response to a sea level highstand at 6500 14 c yr bp ca 7400 cal yr bp soils were buried by expanding wetlands at ca 6000 14 c yr bp a trend that persisted until ca 3400 14 c yr bp ca 3700 cal yr bp over this interval we observe repeated fluctuations between grassland and halophytic vegetation in response to variations in water level and physical chemical conditions resulting from desiccation or flooding events these variations are caused by hydrologic variability in a subhumid dry climatic mean state channel incision occurred between ca 3400 and 2500 14 c yr bp ca 3700 3200 cal yr bp concurrent with sporadic and intermittent sediment deposition at higher elevations of the floodplain the pollen record from the paleochannel infilling indicate grasses accompanied by halophytic taxa between ca 2500 and 800 14 c yr bp 3200 and 700 cal yr bp deposited in a shallow brackish to fresh water body the palynological spectra from sediments deposited sporadically at higher elevations show halophytic vegetation and a trend toward wetland desiccation followed by development of psammophytic communities after ca 1100 14 c yr bp the tops of the alluvial sequences are covered by sand dunes whose modern spectra are characterized by psammophytic vegetation along with exotic tree taxa our results and inferences are consistent with previous studies and provide more detailed insights into the impacts of holocene sea level and climatic variations aspects that are relevant for the coastal pampa grasslands under various scenarios in a warming world

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

late pleistocene relic ultisols and alfisols in an alluvial fan complex in coastal tuscany detailed stratigraphic sedimentary facies and palaeosol analyses were performed on an outcrop on late quaternary deposits in the coastal area of tuscany the outcrop was selected as representative of one of the major quaternary alluvial fan complexes of central italy the ancient cecina river fan and as showing contrasting if related palaeosols the oldest relic palaeosol was identified as an ultisol representative of the most developed soil type normally found as relic soil in italy and about whose possible ages only approximate interpretations presently exist osl dating set the whole succession of sediments palaeosols and geomorphic surfaces into a firm chronological setting as a result evolution of the cecina fan complex in late pleistocene could be fully reconstructed assessment of the age of the relic ultisol produced results contrasting with current interpretations showing how such a soil type can have developed in italian conditions in a relatively short time i e since about mis 5d

upper quaternary palaeoclimates of the mar chiquita area north pampa argentina abstract the mar chiquita shallow lake is the largest water body in argentina located in a quaternary tectonic depression 30 45 s and 62 30 w the southern margin of the depression is dominated by fluvial sediments transported by the rio segundo and aeolian deposits a 65 km wide alluvial fan is the most significant geological unit the sequence of climatic events in the area is i upper pleistocene dry period is4 development of a large sand sea ii complex upper pleistocene humid period is3 first phase of pedogenesis on the aeolian landforms and fluvial deposits marull sands general dissipation of the inherited relief carcarana fm and probable formation of the large alluvial fan lagunilla del plata fm second phase of pedogenesis in a flat landscape during this phase the mar chiquita lake acted as local base level iii late pleistocene dry period is2 lgm deposition of a loess mantle on the surface of the fan tezanos pinto fm iv a subhumid phase 16 000 yr bp redistribution of sand dunes lomita del indio fm and precipitation of pedogenic carbonates in the loess development of a fluvial terrace v younger dryas s l development of deflation hollows associated with lunettes vi hypsithermal humid period general pedogenesis rise of the lake level vii upper holocene dry period deposition of a loess sheet san guillermo fm formation of deflation hollows viii little ice age reduction of the lake surface area and formation of a dune field campo maare sands

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

evolution of 3 d subduction induced mantle flow around lateral slab edges in analogue models of free subduction analysed by stereoscopic particle image velocimetry technique abstract we present analogue models of free subduction in which we investigate the three dimensional 3 d subduction induced mantle flow focusing around the slab edges we use a stereoscopic particle image velocimetry spiv technique to map the 3 d mantle flow on 4 vertical cross sections for one experiment and on 3 horizontal depth sections for another experiment on each section the in plane components are mapped as well as the out of plane component for several experimental times the results indicate that four types of maximum upwelling are produced by the subduction induced mantle flow the first two are associated with the poloidal circulation occurring in the mantle wedge and in the sub slab domain a third type is produced by horizontal motion and deformation of the frontal part of the slab lying on the 660 km discontinuity the fourth type results from quasi toroidal return flow around the lateral slab edges which produces a maximum upwelling located slightly laterally away from the sub slab domain and can have another maximum upwelling located laterally away from the mantle wedge these upwellings occur during the whole subduction process in contrast the poloidal circulation in the mantle wedge produces a zone of upwelling that is vigorous during the free falling phase of the slab sinking but that decreases in intensity when reaching the steady state phase the position of the maximum upward component and horizontal components of the mantle flow velocity field has been tracked through time their time evolving magnitude is well correlated to the trench retreat rate the maximum upwelling velocity located laterally away from the subducting plate is 18 24 of the trench retreat rate during the steady state subduction phase it is observed in the mid upper mantle but upwellings are produced throughout the whole upper mantle thickness potentially promoting decompression melting it could thereby provide a source for intraplate volcanism such as mount etna in the mediterranean the chiveluch group of volcanoes in kamchatka and the samoan hotspot near tonga

slab pull and indentation tectonics insights from 3d laboratory experiments abstract we investigate using 3d laboratory experiments how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions lithospheric plates are modelled by sand silicone plates floating on glucose syrup and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced analogue experiments model the convergence between two lithospheric plates a small continent indenting a large continental plate we show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone slab break off following the subduction of the small continent favours the indentation process because it results in an increasing compression in front of the indenter and extension above the neighbouring oceanic subduction both of them being responsible for the appearance of the indenter like geometry of the plate boundary when the slab does not deform significantly at depth in contrast the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction during which the tectonic regime within the wide continent remains quite homogeneous comparing the presented analogue experiments with the subductions both part of the arabian indenter within eurasia our results suggest that the different tectonic regime on both sides of the arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern anatolia

the interaction of two indenters in analogue experiments and implications for curved fold and thrust belts abstract scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold and thrust belt the experimental set up has two adjacent indenters moving in parallel with a velocity difference the slow indenter moves with a relative velocity ranging from 40 to 80 of that of the fast one in a first experimental series quartz sand and low friction glass beads represent the sediment stack and its basal detachment respectively silicone oil simulates a viscous detachment in the second series of experiments the surface evolution and the spatio temporal strain distribution are derived from particle image velocimetry piv together with the 3d finite structure derived by cutting the models at the end of each experiment this allows the analysis of the structural evolution of the experimental wedges thrusting wedge development depends crucially on the relative velocity when the slow indenter moves with a velocity of more than 55 of the fast indenter a single curved thrust wedge develops the wedge becomes decoupled along strike slip zone at large velocity differences i e when the slow indenter moves slower than 55 of the faster indenter consequently the thrust front is strongly curved at high 55 60 and smoothly curved at low velocity differences 70 80 in all cases curvature increases during indentation along the most strongly curved portion of the thrust wedge the transfer zone rises particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front this implies distant effects of wedge growth active hundreds of kilometres along strike of orogens silicone oil as a detachment induces a low angle wedge which is less curved than in the glass beads experiments and shows variable thrust vergence with fore and back thrusts we compare our experimental results with the curved fold and thrust belts of the tajik basin in front of the hindu kush and pamir indenters our results are able to explain several first order features

rheological properties of paraffin as an analogue material for viscous crustal deformation the rheological stratification induced by temperature variations within the crust requires analogue materials with temperature sensitive viscosity to properly simulate the change of mechanical properties with depth rheological calibration experiments on commercial paraffin wax with melting point of 53 1 c show that this material is a nonlinear fluid 1 6 n 2 1 for homologous temperatures t tm 0 70 and an approximately newtonian fluid 1 0 n 1 3 for t tm 0 70 the decrease in the stress exponent n is probably associated with the phase transition of paraffin effective viscosity values are strongly temperature dependent varying by nine orders of magnitude from 1010 to 10 pa s in the temperature range between 30 and 52 c the rheological properties of paraffin make this material useful for modelling crustal rheology and tectonic processes when linear dimensions and time scale down by a factor of 106 and 1011 respectively

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

application of open source photogrammetric software micmac for monitoring surface deformation in laboratory models quantifying deformation is essential in modern laboratory models of geological systems this paper presents a new laboratory monitoring method through the implementation of the open source software micmac which efficiently implements photogrammetry in structure from motion algorithms critical evaluation is provided using results from two example laboratory geodesy scenarios magma emplacement and strike slip faulting micmac automatically processes images from synchronized cameras to compute time series of digital elevation models dems and orthorectified images of model surfaces micmac also implements digital image correlation to produce high resolution displacements maps the resolution of dems and displacement maps corresponds to the pixel size of the processed images using 24 mp cameras the precision of dems and displacements is 0 05 mm on a 40 40 cm surface processing displacement maps with matlab scripts allows automatic fracture mapping on the monitored surfaces micmac also offers the possibility to integrate 3 d models of excavated structures with the corresponding surface deformation data the high resolution and high precision of micmac results and the ability to generate virtual 3 d models of complex structures make it a very promising tool for quantitative monitoring in laboratory models of geological systems

contrasting tectono metamorphic evolution of orogenic lower crust in the bohemian massif a numerical model abstract the bohemian massif located at the eastern margin of the european variscan belt is characterised by an exceptional accumulation of felsic high pressure granulites the petrological structural and geochronological studies of this region revealed systematic differences between the tectonometamorphic evolution of the southern moldanubian and northern west sudetes parts of the orogen two contrasting tectonic scenarios have been proposed gravity driven vertical mass exchanges followed by continental indentation in the moldanubian domain and crustal scale folding leading to gneiss dome formation in the west sudetes we present a numerical model in order to correlate the apparent differences between these two regions with the variations in the dynamics of the modelled system we model two colliding blocks an orogenic root where a felsic lower crust is overlain by a mafic layer and a middle crust and a continental indentor we examine the role of the rate of convergence of the two blocks radiogenic heat production within the felsic lower crust and efficiency of erosion the prograde part of the metamorphic evolution is controlled by the rate of convergence and the peak temperature depends on the heat production the retrograde evolution is controlled mostly by erosional processes in the models where the material is weakened due to the heating in the felsic lower crust the gravitational instability of the mafic and felsic layers causes their complete vertical exchange followed by a flow above the indentor in colder and or faster models the thickening is dominated by the buckling of the mafic layer these two styles of deformation i e gravity dominated and fold dominated models correspond to the structures observed in the moldanubian and the west sudetes moreover the calculated pressure temperature paths of the felsic lower crust are in agreement with available data

a review of late quaternary inland dune systems of south america east of the andes abstract inland dune systems of south america occur in a variety of environmental settings under different climatic conditions from humid subhumid to semiarid arid this contribution provides the state of the art on dune research of inland systems east of the andes tropical northern 10 n 10 s including the dune fields of llanos del orinoco and the amazonian basin are mainly formed from parabolic blowout or deflation basins and linear dunes developed on river floodplains aeolian activity was reported to occur near the late pleistocene holocene boundary in llanos del orinoco over the last 17 ka in the branco river basin and 32 6 ka in the negro river basin both in the amazonian region in general the attributed aeolian origin is controversial the morphology difficult to determine and the chronology still extremely limited and rather debatable in some cases the southern tropical region 10 s 22 s includes aeolian systems situated across the extensive lowlands of the gran chaco and those located in fluvial basins related to the cratonic brazilian shield sao francisco river pantanal and mato grosso the oldest barchanoid barchan ridges at the gran chaco were dated 36 33 ka and subsequent aeolian sand accumulation occurred at 18 ka 14 12 ka 10 9 ka and mid to late holocene times parabolic dunes at the sao francisco river floodplain show an oldest episode generated between 28 and 11 ka followed by eolian activity during the early to mid holocene no chronological data is available for the linear and lunette dunes described at the pantanal linear ridges were distinguished in the upper parana river mato grosso with associated sand accumulation at different intervals of the holocene the last reviewed region is the andean piedmont and western pampas at subtropical eastern south america comprising a large variety of dune morphologies barchan barchanoid linear parabolic transverse and lunette dunes deflation basins and sand sheets luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the holocene the general understanding on the dynamic of south american dune systems is hampered by the paucity of chronological information and the representativeness of some dune records whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies

north atlantic forcing of amazonian precipitation during the last ice age the last glacial period was marked by rapid reorganizations of oceanic and atmospheric circulation speleothem records from the amazon basin suggest that precipitation variability was linked to these events the last glacial period was marked by multiple abrupt reorganizations of ocean and atmosphere circulation1 on thousand year timescales slowing of the atlantic meridional overturning circulation was associated with cooling in the high northern latitudes whereas strengthened circulation was linked to northern warming1 2 in the tropics these millennial scale events were primarily reflected in altered patterns of precipitation3 these hydrologic fluctuations induced ecological changes in the atlantic seaboard and the high andes2 but less is known about the amazon basin here we reconstruct precipitation over amazonian ecuador over the past 94 000 years using a 18o record from speleothems collected in santiago cave in western amazonia we interpret the variability of the 18o record as changes in the source and amount of precipitation with the exception of the period between 40 000 and 17 000 years ago abrupt high frequency changes coincide with shifts in north atlantic circulation indicating a high latitude influence on amazonian precipitation over millennial timescales on longer timescales the record shows a relationship to precessional changes in the earth s orbit in light of the lack of extreme aridity in our records we conclude that ecosystems in western amazonia have not experienced prolonged drying over the past 94 000 years

3d numerical modeling of mantle flow crustal dynamics and magma genesis associated with slab roll back and tearing the eastern mediterranean case interactions between subduction dynamics and magma genesis have been intensely investigated resulting in several conceptual models derived from geological geochemical and geophysical data to provide physico chemical constraints on these conceptual models self consistent numerical simulations containing testable thermo mechanical parameters are required especially considering the three dimensional 3d natural complexity of subduction systems here we use a 3d high resolution petrological and thermo mechanical numerical model to quantify the relative contribution of oceanic and continental subduction collision slab roll back and tearing to magma genesis and transport processes our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3d slab dynamics and related asthenospheric flow moreover the decrease of the bulk lithospheric strength induced by mantle and crust derived magmas promotes the propagation of strike slip and extensional fault zones through the overriding crust as response to slab roll back and continental collision reduction of the lithosphere asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust similarities between our modeling results and the late cenozoic tectonic and magmatic evolution across the eastern mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region which in turn promotes lithospheric deformation by mantle drag via melt induced weakening effects

properties of granular analogue model materials a community wide survey we report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories we determined physical characteristics such as bulk density grain size distribution and grain shape and performed ring shear tests to determine friction angles and cohesion and uniaxial compression tests to evaluate the compaction behaviour mean grain size of the materials varied between c 100 and 400 m analysis of grain shape factors shows that the four different classes of granular materials 14 quartz sands 5 dyed quartz sands 4 heavy mineral sands and 3 size fractions of glass beads can be broadly divided into two groups consisting of 12 angular and 14 rounded materials grain shape has an influence on friction angles with most angular materials having higher internal friction angles between c 35 and 40 than rounded materials whereas well rounded glass beads have the lowest internal friction angles between c 25 and 30 we interpret this as an effect of intergranular sliding versus rolling most angular materials have also higher basal friction angles tested for a specific foil than more rounded materials suggesting that angular grains scratch and wear the foil most materials have an internal cohesion in the order of 20 100 pa except for well rounded glass beads which show a trend towards a quasi cohesionless c 20 pa coulomb type material the uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains we interpret this to be related to the initial packing density after sifting which is higher for rounded grains than for angular grains ring shear test data show that angular grains undergo a longer strain hardening phase than more rounded materials this might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains

pedodiversity analysis at large scales an example of three fluvial terraces of the henares river central spain abstract this paper presents the results of the application of richness and diversity indices and the fitting of four probabilistic distribution models to a soil chronosequence developed on the fluvial terraces of the henares river ne madrid as a means to analyse the soil mantle evolution of the valley during the quaternary richness area relationships were also investigated calculations were performed considering individuals i e pedons and the area covered by a given soil type at different hierarchy levels of the usda taxonomic classification great group subgroup and family as well as for diagnostic horizons abundance of great groups and subgroups richness or pedorichness increases from low young to high old terraces it has also been found that the higher the detail in the classification the higher the pedodiversity values diagnostic horizons accounted for the genetic pedodiversity its value decreases with soil development in the first meter of the solum this trend changes with increasing observation depth therefore genetic pedorichness and pedodiversity increase in this example with the age of geomorphologic surfaces however an appropriate quantification of the genetic diversity should consider the entire solum depth it is also shown that pedodiversity increases with the area considered on the other hand the fit of sampled areas to the probabilistic distribution models used by ecologists is less conclusive regarding richness area relationships the low and middle terraces fitted a logarithmic function while the high terrace fitted a power model in agreement with the ecological literature on biotaxa area relationships

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

does subduction induced mantle flow drive backarc extension abstract backarc extension is a characteristic feature of many narrow subduction zones seismological and geochemical studies imply the occurrence of mantle flow around the narrow subducting slabs previous 3d models suggested that backarc extension is related to subduction induced toroidal mantle flow the physical viability of this mechanism however has never been tested using laboratory based geodynamic models in this work we present dynamic laboratory models of progressive subduction in three dimensional 3d space that were carried out to test this mechanism to achieve this we have used a stereoscopic particle image velocimetry spiv technique to map simultaneously overriding plate deformation and 3d subduction induced mantle flow underneath and around an overriding plate the results show that the strain field of the overriding plate is characterized by the localization of an area of maximum extension within its interior at 300 500 km from the trench the position of maximum extension closely coincides within 2 cm scaling to 100 km with that of the maximum trench normal horizontal mantle velocity and velocity gradient measured at a scaled depth of 15 25 km below the base of the overriding plate and the maximum horizontal gradient of the vertical mantle velocity gradient we propound that in narrow subduction zones backarc extension in the overriding plate is mainly a consequence of the trench normal horizontal gradients of basal drag force at the base of the overriding plate such shear force gradients result from a horizontal gradient in velocity in the mantle below the base of the lithosphere induced by slab rollback calculations based on our models indicate a tensional horizontal trench normal deviatoric stress in the backarc region scaling to 28 8 mpa while the overriding plate trench normal stress resulting from the horizontal component of the trench suction force is about an order of magnitude smaller scaling to 2 4 3 6 mpa

vegetational history of the late glacial holocene transition in the grasslands of eastern argentina abstract palynological records from eight sites located in the eastern plains of argentina from the humid pampa in the east to the xerophytic woodland dry pampa ecotone in the west allow a regional reconstruction of the vegetation of late glacial holocene transition fossil pollen records were interpreted in terms of palaeoenvironmental information using the modern pollen vegetation climate relationship as an analogue although an exact analogue does not exist today late glacial vegetation consisted mostly of psammophytic steppe in large areas of the central and south western pampa grassland which in the south west is associated with a shrub steppe suggesting subhumid dry to semi arid climatic conditions the replacement of dry steppe by humid grassland and the rapid evolution of pond environments during the early holocene starting during the late glacial holocene transition suggests a shift towards subhumid to humid climate conditions the late glacial holocene transition is indicated in the pollen records by repeated abrupt changes in the proportions and concentrations of some taxa such as brassicaceae asteraceae and carduus type in the modern vegetation they represent species of common occurrence in human induced disturbance habitats suggesting an environment that was subject to frequent natural disturbance such as rapid and repeated flooding episodes that inundated the depressions along the valley floodplains caused by unusual rainfall events some species of carduus may have been native and not introduced by the europeans suggesting that late glacial vegetation of the pampa grasslands may account for the abundance of ruderal species of special interest is the presence of myrtaceae in some pollen assemblages between 11 000 and 9000 yr b p at present myrtaceae are not part of the natural vegetation in the pampa grassland their presence in the fossil pollen records may be interpreted as local deposition instead of extra regional origin myrtaceae formed part of the psammophytic steppe and after late glacial holocene transition they disappeared from the regional flora perhaps due to the climatic change that occurred at the beginning of the holocene it is the most significant cause of extending the area of some pampa grassland taxa but it may have reduced the area for others of the late glacial vegetation at least myrtaceae were probably not able to adapt to the new habitats and hence disappeared from the regional flora at the pleistocene holocene transition although other plants may have disappeared as well these cannot be identified because pollen from these plants cannot be differentiated morphologically during the late glacial holocene transition communities with no modern counterparts probably formed and disappeared

palaeomagnetic and structural constraints on 90 anticlockwise rotation in sw mongolia during the permo triassic implications for altaid oroclinal bending preliminary palaeomagnetic results abstract new and published paleomagnetic measurements from trans altai and south gobi zones in south mongolia document large tectonic motions in between late carboniferous and triassic magnetic inclinations confirm equatorial position of south mongolian terranes in late carboniferous permian times the evolution of magnetic declinations indicates 90 anticlockwise rotation in between latest carboniferous and early triassic of all studied tectonic units around the eulerian pole located close to axis of mongolian orocline the anticlockwise rotation continues in triassic being accompanied by a major drift to the north the structural and published geochronological data suggest carboniferous e w shortening of the whole region resulting in n s trend of all continental and oceanic geological units followed by orthogonal n s shortening during late permian to early jurassic both paleomagnetic and geological data converge in a tectonic model of oroclinal bending of mongolian ribbon continent westerly back arc oceanic domain and mongol okhotsk subduction zone to the east the oroclinal bending model is consistent with the coincidence of the eulerian pole of rotation with the structural axis of mongolian orocline in addition the mesozoic collisional tectonics is reflected by late remagnetizations due to formation of wide deformation fronts and hydrothermal activity

migmatites granites and orogeny flow modes of partially molten rocks and magmas associated with melt solid segregation in orogenic belts abstract this paper presents a model for the genesis of migmatites and granites during orogenic evolution based on the analysis of several phanerozoic crustal segments and a review of the physical properties of partially molten rocks and magmas this model inventories the modes of bulk flow of partially molten rocks and magmas and the mechanisms of melt solid segregation for each mode partial melting of rocks is associated with a strength decrease of two to three orders of magnitude leading to strain partitioning expressed by channel flow driven either by forces related to plate tectonics vertical channel flow or by the gravity force associated with lateral variations of crustal thicknesses horizontal channel flow although the structural characteristics of migmatites indicate that deformation plays a role in melt migration the emplacement of laccoliths of leucogranites above migmatites attests to the efficiency of the buoyancy force another decrease in apparent strength of about ten orders of magnitude is associated with the loss of continuity of the solid framework marking the transition from partially molten rocks to magmas the breakdown of the solid framework also allows for settling of the solid in suspension increasing the buoyancy of the remaining magma accordingly domes cored by diatexites former heterogeneous magmas and mantled by metatexites former partially molten rocks are interpreted as gravitational instabilities driven by the relative buoyancy of the magma and permitted by the weakness of the partially molten rocks this model provides a first order framework to elucidate the development of a crustal scale horizontal layering during the evolution of orogenic belts that are affected by partial melting in this case the middle crust is dominated by migmatites with domes cored by diatexites and mantled by metatexites that correspond to a partially molten and magmatic zone respectively the granitic dikes and sills and the associated laccoliths of leucogranites correspond to an intrusive zone overlying the partially molten zone the refractory lower crust is potentially in part formed by accumulation of solids segregated from the overlying heterogeneous magmas

impact of bolivian paleolake evaporation on the δ18o of the andean glaciers during the last deglaciation 18 5 11 7 ka diatom inferred δ18o values and hydro isotopic modeling abstract during the last deglaciation the bolivian altiplano 15 23 s 66 70 w was occupied by paleolake tauca covering at least 51 000 km 2 at its maximum highstand between 16 5 and 15 ka twenty five hundred years later after a massive regression a new transgressive phase produced paleolake coipasa smaller than tauca and restricted to the southern part of the basin these paleolakes were overlooked at the west by the sajama ice cap the latter provides a continuous record of the oxygen isotopic composition of paleo precipitation for the last 25 ka contemporaneously to the end of paleolake tauca around 14 3 ka the sajama ice cap recorded a significant increase in ice oxygen isotopic composition 18 o ice this paper examines to what extent the disappearance of lake tauca contributed to precipitation on the sajama summit and this specific isotopic variation the water 18 o values of paleolakes tauca and coipasa 18 o lake were quantitatively reconstructed from 18 5 to 11 7 ka based on diatom isotopic composition 18 o diatoms and ostracod isotopic composition 18 o carbonates retrieved in lacustrine sediments at a centennial time scale a strong trend appears abrupt decreases of 18 o lake during lake fillings are immediately followed by abrupt increases of 18 o lake during lake level stable phases the highest variation occurred at 15 8 ka with a 18 o lake decrease of about 10 concomitant with the lake tauca highstand followed 400 years later by a 7 increase in 18 o lake a simple hydro isotopic modeling approach reproduces consistently this rapid decrease increase feature moreover it suggests that this unexpected re increase in 18 o lake after filling phases can be partly explained by an equilibration of isotopic fluxes during the lake steady state based on isotopic calculations during lake evaporation and a simple water stable isotopes balance between potential moisture sources at sajama advection versus lake evaporation we show that total or partial evaporation from 5 to 60 of paleolake tauca during its major regression phase at 14 3 ka could explain the pronounced isotopic excursion at sajama ice cap these results suggest that perturbations of the local hydrological cycle in lacustrine areas may substantially affect the paleoclimatic interpretation of the near by isotopic signals e g ice core or speleothems

advanced strain and mass transfer analysis in crustal scale oroclinal buckling and detachment folding analogue models abstract the piv particle image velocimetry method became a standard tool for the calculation of displacement fields in physical geodynamic models for understanding the deformation dynamics of geodynamic models in our study we implemented several post processing algorithms on the derived displacement field and calculated the velocity and strain rate components such as the divergence of the velocity field vorticity and shear strain rate in the model of oroclinal buckling we focused on strain analysis of the upper crust and correlated the shear strain rate vorticity and divergence anomalies with visual deformation patterns in the upper crust the divergence of velocity fields in these models correspond to the pop up and pop down belts oriented along the axial trace of the oroclinal bends high shear strain rate domains correlate with horizontal isovolumic shear zones alongside these belts while vorticity shows rotational trend of fold axial traces of the pop up and pop down belts around orocline inflection in another series of models we simulated the development of melt cored crustal scale detachment folds and employed the same set of parameters to investigate the ductile deformation visible in side view of the model domain we developed a method that allows tracing the divergence in subcells locked on target subdomains we tracked and quantified melt flow between the melt source area at the bottom of the model and progressively developing folds this mass transfer analysis revealed polyphase fold evolution where initial fold perturbations quickly amplify as the melt accumulates in the triangular hinge sector below and between the rotating fold limbs while the early amplification leads to decompression driving the melt into the hinge zone area between the limbs the fold lock up stage and continued attenuation of the vertical limbs is associated with melt expulsion from the fold interlimb domain back into the source layer where it can be transferred laterally to the foreland

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

continental delamination insights from laboratory models 1 one of the major issues of the evolution of continental lithospheres is the detachment of the lithospheric mantle that may occur under certain conditions and its impact on the surface in order to investigate the dynamics of continental delamination we performed a parametric study using physically scaled laboratory models the adopted setup is composed of a three layers visco elastic body analog for upper crust lower crust lithospheric mantle locally thickened thinned to simulate a density anomaly lithospheric root and an adjacent weak zone lying on a low viscosity material simulating the asthenosphere the results emphasize the interplay between mantle flow deformation surface topography and plate motion during a three phases process 1 a slow initiation phase controlled by coupling and bending associated with contraction and dynamic subsidence 2 lateral propagation of the delamination alongside with extension and a complex topographic signal controlled by coupling and buoyancy while poloidal mantle flow develops around the tip of the delaminating lithospheric mantle and 3 a late phase characterized by a counterflow that triggers retroward motion of the whole model a semiquantitative study allows us to determine empirically two parameters 1 an initiation parameter that constrains the propensity of the delamination to occur and correlates with the duration of the first stage 2 a buoyancy parameter characterizing the delamination velocity during late stages and therefore its propensity to cease finally we point out similarities and differences with the sierra nevada california usa in terms of topography deformation and timing of delamination

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

nature and causes of quaternary climate variation of tropical south america abstract this selective review of the quaternary paleoclimate of the south american summer monsoon sasm domain presents viewpoints regarding a range of key issues in the field many of which are unresolved and some of which are controversial 1 el nino southern oscillation variability while the most important global scale mode of interannual climate variation is insufficient to explain most of the variation of tropical south american climate observed in both the instrumental and the paleoclimate records 2 significant climate variation in tropical south america occurs on seasonal to orbital i e multi millennial time scales as a result of sea surface temperature sst variation and ocean atmosphere interactions of the tropical atlantic 3 decadal scale climate variability linked with this tropical atlantic variability has been a persistent characteristic of climate in tropical south america for at least the past half millennium and likely far beyond 4 centennial to millennial climate events in tropical south america were of longer duration and perhaps larger amplitude than any observed in the instrumental period which is little more than a century long in tropical south america these were superimposed upon both precession paced insolation changes that caused significant variation in sasm precipitation and eccentricity paced global glacial boundary conditions that caused significant changes in the tropical south american moisture balance as a result river sediment and water discharge increased and decreased across tropical south america lake levels rose and fell paleolakes arose and disappeared on the altiplano glaciers waxed and waned in the tropical andes and the tropical rainforest underwent significant changes in composition and extent to further evaluate climate forcing over the last glacial cycle 125 ka we developed a climate forcing model that combines summer insolation forcing and a proxy for north atlantic sst forcing to reconstruct long term precipitation variation in the sasm domain the success of this model reinforces our confidence in assigning causation to observed reconstructions of precipitation in addition we propose a critical correction for speleothem stable oxygen isotopic ratios which are among the most significant of paleoclimate proxies in tropical south america for reconstruction of variation of paleo precipitation or sasm intensity however it is already well known that any particular 18o value observed in speleothem carbonate is affected by two processes that have nothing to do with changes in precipitation amount the influence of temperature on carbonate water isotopic fractionation in the cave and the influence of changing 18o of seawater quantitatively accounting for both artifacts can significantly alter the interpretations of speleothem records in tropical south america both adjustments act in the same direction and have the tendency to increase the true amplitude of the paleo hydrologic signal but by different amounts in glacial and inter glacial stages these corrections have even graver implications for the interpretation of tropical northern hemisphere speleothem records e g chinese speleothems where the combined adjustments tend to decrease or even eliminate the true signal amplitude

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

crustal flow modes in large hot orogens abstract crustal scale channel flow numerical models support recent interpretations of himalayan tibetan tectonics proposing that gravitationally driven channel flows of low viscosity melt weakened middle crust can explain both outward growth of the tibetan plateau and ductile extrusion of the greater himalayan sequence we broaden the numerical model investigation to explore three flow modes homogeneous channel flow involving laterally homogeneous crust heterogeneous channel flow involving laterally heterogeneous lower crust that is expelled and incorporated into the mid crustal channel flow and the hot fold nappes style of flow in which mid lower crust is forcibly expelled outward over a lower crustal indentor to create fold nappes that are inserted into the mid crust the three flow modes are members of a continuum in which the homogeneous mode is driven by gravitational forces but requires very weak channel material the hot fold nappe mode is driven tectonically by for example collision with a strong crustal indentor and can occur in crust that is subcritical for homogeneous flows the heterogeneous mode combines tectonic and gravitationally driven flows preliminary results also demonstrate the existence and behaviour of mid crustal channels during advancing and retreating dynamical mantle lithosphere subduction an orogen temperature magnitude t m diagram is proposed and the positions of orogens in t m space that may exhibit the flow modes are described together with the characteristic positions of a range of other orogen types

lake highstands on the altiplano tropical andes contemporaneous with heinrich 1 and the younger dryas new insights from 14 c u th dating and δ 18 o of carbonates this study provides new geochronological and stable isotope constraints on late pleistocene fluctuations in lake level that occurred in the closed watershed of the central altiplano between 25 and 12 ka u series isochrons and 14 c ages from carbonates are used to confirm and refine the previous chronology published placzek et al 2006b our new data support three successive lake highstands during the late pleistocene i the lake sajsi cycle from 25 to 19 ka that culminated at 3670 m at about 22 ka almost synchronously with the global last glacial maximum ii the lake tauca cycle that lasted from 18 to 14 5 ka and was characterized by the highest water level reached at least 3770 m from 16 5 to 15 ka iii the lake coipasa cycle from 12 5 to 11 9 ka that reached an elevation of 3700 m 42 m above the elevation of the salar de uyuni 3658 m these high amplitude lake level fluctuations are in phase with the cold warm oscillations that occurred in the north atlantic and greenland during the late pleistocene heinrich 1 bolling allerod younger dryas such temporal coincidence supports the hypothesis that wet events recorded in the central altiplano are controlled by the northesouth displacement of the inter tropical convergence zone resulting from changes in the meridional temperature gradient finally the oxygen isotope ratios measured in these lacustrine carbonates allows for calculation of the 18 o value of paleolake waters estimates of water 18 o v smow are 2 8 0 7 for lake tauca and 1 6 0 9 for lake coipasa these data are used to constrain changes in lake hydrology and can be interpreted to indicate that the proportion of precipitation arising from local water recycling was less than 50

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

changes in structural style of normal faults due to failure mode transition first results from excavated scale models abstract the effects of failure mode transition from tensile to shear on structural style and fault zone architecture have long been recognized but are not well studied in 3d although the two modes are both common in the upper crust of earth and terrestrial planets and are associated with large differences in transport properties we present a simple method to study this in physical scale models of normal faults using a cohesive powder embedded in cohesionless sand by varying the overburden thickness the failure mode changes from tensile to hybrid and finally to shear hardening and excavating the cohesive layer allows post mortem investigation of 3d structures at high resolution we recognize two end member structural domains that differ strongly in their attributes in the tensile domain faults are strongly dilatant with steep open fissures and sharp changes in strike at segment boundaries and branch points in the shear domain fault dips are shallower and fault planes develop striations map view fault traces undulate with smaller changes in strike at branches these attributes may be recognized in subsurface fault maps and could provide a way to better predict fault zone structure in the subsurface

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

stable isotope analyses on the last 30 ka molluscan fauna from pampa grassland bonaerense region argentina abstract fossil and living shells of terrestrial and freshwater molluscs collected from various sites in the bonaerense and patagonia regions of argentina were analysed for their stable isotope content as a possible tool for palaeoclimatic and palaeoenvironmental reconstruction the oxygen isotope composition of calcareous shell from freshwater samples was interpreted in terms of a change in moisture condition and the related evaporative effect on surficial bodies of water linked to a climatic shift the carbon isotope composition mainly records changes in biological productivity interpretation of the isotopic composition of the land snail carbonate is more complex and worldwide data from living shells have been used to decipher to some extent the palaeoenvironmental record contained in their isotopic composition overall the interpretations deduced from isotopic data of land snails as well as from nearby freshwater molluscs are quite comparable the isotopic data suggest that arid conditions occurred between 35 and 15 ka b p and warmer conditions around 35 25 ka b p a shift toward a new phase comparable with the present meteorological and climatic situation probably began around 9 ka b p and it was linked to some short but severe climatic fluctuations thus suggesting that high climatic stress characterised this period moreover a trend toward slightly arid conditions is suggested by isotopic data possibly sometimes after 5 ka the differences arising from the geographical location and the short duration of each single series studied still hamper an extensive interpretation of the isotopic data

a 2 300 year long annually resolved record of the south american summer monsoon from the peruvian andes decadal and centennial mean state changes in south american summer monsoon sasm precipitation during the last 2 300 years are detailed using an annually resolved authigenic calcite record of precipitation 18o from a varved lake in the central peruvian andes this unique sediment record shows that 18o peaked during the medieval climate anomaly mca from a d 900 to 1100 providing evidence that the sasm weakened considerably during this period minimum 18o values occurred during the little ice age lia between a d 1400 and 1820 reflecting a prolonged intensification of the sasm that was regionally synchronous after the lia 18o increased rapidly particularly during the current warm period cwp a d 1900 to present indicating a return to reduced sasm precipitation that was more abrupt and sustained than the onset of the mca diminished sasm precipitation during the mca and cwp tracks reconstructed northern hemisphere and north atlantic warming and a northward displacement of the intertropical convergence zone itcz over the atlantic and likely the pacific intensified sasm precipitation during the lia follows reconstructed northern hemisphere and north atlantic cooling el nino like warming in the pacific and a southward displacement of the itcz over both oceans these results suggest that sasm mean state changes are sensitive to itcz variability as mediated by western hemisphere tropical sea surface temperatures particularly in the atlantic continued northern hemisphere and north atlantic warming may therefore help perpetuate the recent reductions in sasm precipitation that characterize the last 100 years which would negatively impact andean water resources

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

lithospheric scale structures from the perspective of analogue continental collision abstract analogue models were employed to investigate continental collision addressing the roles of 1 a suture zone separating different crustal blocks 2 mid crustal weak layers and 3 mantle strengths these models confirmed that low amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and or lithospheric mantle with increasing shortening bivergent thrusts formed across the brittle layers equivalent to upper crust at inflection points of the buckles while ductile layers lower crust and mantle continued being folded the resulting geometries displayed pop ups and pop downs above the boundaries sutures between blocks further shortening led to wider thrust bounded deformation zones belts in front of the stronger blocks identified as effective indenters during shortening upward extrusion into belts allowed exhumation of deep material weak layers enhanced strain localisation these modelling results have similarity in large scale structures of modern orogens and are relevant to the understanding of natural collisional processes

assessing links between late holocene climate change and paleolimnological development of pena lagoon using opal phytoliths physical and geochemical proxies abstract opal phytolith geochemical and sedimentological data from two cores taken in pena lagoon a small water body on the atlantic shore of uruguay are presented in this paper the choice of this specific sampling location aimed to obtain high resolution records to infer late holocene environmental and climatic changes in southeastern uruguay in order to improve previous models for early and middle holocene the combined record of two cores extends to 2500 14c bp with a sedimentation rate ranging between 0 6 and 2 mm y 1 a multiproxy approach allowed the identification of changes in dynamics particularly organic matter and sediment input variability from the watershed with this information differences in the amount and extent of environmental signals were evaluated and a comprehensive climate change model was generated especially for the last 1500 years three main climatic events were distinguished the oldest which lasted until 700 ad was characterized by temperate and humid conditions the second extended until 1200 ad and warmer and wetter conditions were inferred but also a colder and drier pulse was observed in between this second event was assigned to the warm medieval period wmp during the third event assigned to the little ice age lia which extended until the present a high variability in climate was observed but also three dry cold phases reaching their maxima by 1300 1600 and 1900 ad were inferred

a review of statistical chronology models for high resolution proxy based holocene palaeoenvironmental reconstruction abstract in this paper we explain the background workings and results obtained from three recently developed statistical age depth models implemented in freely available general purpose software packages bpeat oxcal and bchron these models aim to reconstruct the sedimentation rate in a single core typically lake peat or ocean given a limited number of scientific date estimates usually radiocarbon and fixed depths most importantly they provide a suitably qualified estimate of the uncertainty in the age depth chronology and thus can be used in a variety of applications we perform a large data driven study of the three models and discuss their general utility in chronology construction for palaeoenvironmental research

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

the ages and soils of two levels of rana surfaces in central spain abstract the geomorphology of two ranas and a specimen soil profile on each have been studied in the province of guadalajara central spain the ranas were first delineated on an aerial photograph then examined in the field for further identification and for the preparation of topographic profiles two soil profiles were described and sampled by horizons analyses were made of the samples for particle size distribution ph cation exchange relations and organic matter plus some observations on mineralogy of clay and fine sand fractions results of the study support earlier suggestions that the younger ran asurface s 1 is of donau age middle villafranchian but indicate that the second s 2 should be assigned to the middle upper pliocene lower villafranchian the soil profiles were found to be an alfisol on the younger and an ultisol on the older rana which is consistent with a greater age for the latter

quantitative 3d strain analysis in analogue experiments simulating tectonic deformation integration of x ray computed tomography and digital volume correlation techniques abstract the combination of scaled analogue experiments material mechanics x ray computed tomography xrct and digital volume correlation techniques dvc is a powerful new tool not only to examine the 3 dimensional structure and kinematic evolution of complex deformation structures in scaled analogue experiments but also to fully quantify their spatial strain distribution and complete strain history digital image correlation dic is an important advance in quantitative physical modelling and helps to understand non linear deformation processes optical non intrusive dic techniques enable the quantification of localised and distributed deformation in analogue experiments based either on images taken through transparent sidewalls 2d dic or on surface views 3d dic x ray computed tomography xrct analysis permits the non destructive visualisation of the internal structure and kinematic evolution of scaled analogue experiments simulating tectonic evolution of complex geological structures the combination of xrct sectional image data of analogue experiments with 2d dic only allows quantification of 2d displacement and strain components in section direction this completely omits the potential of ct experiments for full 3d strain analysis of complex non cylindrical deformation structures in this study we apply digital volume correlation dvc techniques on xrct scan data of solid analogue experiments to fully quantify the internal displacement and strain in 3 dimensions over time our first results indicate that the application of dvc techniques on xrct volume data can successfully be used to quantify the 3d spatial and temporal strain patterns inside analogue experiments we demonstrate the potential of combining dvc techniques and xrct volume imaging for 3d strain analysis of a contractional experiment simulating the development of a non cylindrical pop up structure furthermore we discuss various options for optimisation of granular materials pattern generation and data acquisition for increased resolution and accuracy of the strain results three dimensional strain analysis of analogue models is of particular interest for geological and seismic interpretations of complex non cylindrical geological structures the volume strain data enable the analysis of the large scale and small scale strain history of geological structures

the mar chiquita lake an indicator of intraplate deformation in the central plain of argentina abstract the mar chiquita saline lake is located in the lowest part of one of the largest endorreic saline basins of south america with a surface area of 6000 6500 km2 the lake is located in a tectonic depression with an asymmetric cross section the sierras pampeanas foothills with altitudes near 1500 m are to the west and a 100 m topographic high san guillermo high is to the east whose western border is bounded by a buried middle pleistocene fault the tostado selva fault the main tributary of the lake is the dulce river which flows from north to south the southward flow of the river was impeded by an obstacle that closed the dulce valley generating the mar chiquita lake the megafans of the primero segundo and tercero rivers deposited a large amount of sediment against the faulted border of the san guillermo high generating an obstacle that impeded the normal flow of the rivers and diverted the dulce and the salado rivers to their present positions precise data concerning the age of the impounding of mar chiquita does not exist but lacustrine conditions are undoubtedly younger than the uplift of the san guillermo high which occurred in the middle pleistocene the well preserved dry valley of the dulce river located southward of mar chiquita is still visible in satellite images and confirms the youth of the impounding the observations introduced in this paper allow us to understand the origin of a significant feature of the central plains of south america the generation of mar chiquita lake and upstream wetlands produced a pronounced environmental change in the arid chaco pampeana plain which favored human life by introducing changes in vegetation and fauna

structural constraints on the evolution of the central asian orogenic belt in sw mongolia we provide a detailed description of the structures along a 300 km long and 50 km wide transect across the central asian orogenic belt caob in southwestern mongolia covering the precambrian dzabkhan continental domain with overthrust neoproterozoic ophiolites in the north lake zone a silurian devonian passive margin association gobi altai zone and oceanic domain trans altai zone in the center and a continental area south gobi zone in the south structural analysis suggests late cambrian collapse of the thickened lake zone continental crust leading to stretching of the lithosphere and followed by silurian devonian formation of oceanic crust in the trans altai domain subsequent emplacement of devonian carboniferous and late carboniferous magmatic arcs occurred on the gobi altai and south gobi zone crusts respectively during e w shortening finally the entire system was affected by n s convergence from the permian to jurassic leading to heterogeneous shortening of the orogenic domain the model best fitting these observations is one of generalized westward drift of the tuva mongol dzabkhan baydrag ribbon continents during the silurian devonian associated with westward subduction of the mongol okhotsk ocean and sequential growth of syn convergent magmatic arcs back arc basins opened during this period in the area of the western paleoasian ocean the present day shape of the caob in southern mongolia was probably formed during permian to mesozoic anticlockwise rotation and folding of the tuva mongol dzabkhan baydrag continental ribbons combined with a strike slip transpressional reactivation of ancient transform boundaries in the paleoasian oceanic domain all continental and oceanic crustal domains were reactivated and intensely deformed during this convergence in a style controlled by crustal rheology and a heterogeneous permian magmatic thermal input the sequence of tectonic events is tested against published paleomagnetic data paleogeographic reconstructions and tectonic models leading to a revised model for the accretion of juvenile crust to a continental margin in the caob of southern mongolia

mid holocene paleoenvironments in northwestern argentina main patterns and discrepancies abstract this paper summarizes the available paleoenvironmental information for the mid holocene in northwestern argentina in order to systematize a multi scale scenario for human adaptation in the area the main results of the studies carried out by several research teams that have studied the conditions during this period in the tropical andean region are described and compared taking into account their geographical setting the proxies involved and their particular space time resolution the paleoenvironmental situation prior to the onset of mid holocene conditions i e starting at the late glacial maximum is summarized to estimate the nature and extent of the changes occurred during this period paleoenvironmental results their characteristics and interpretation are also considered a general trend towards an aridization process that fostered a hydrologic stress process is traceable along the mid holocene in northwestern argentina and the tropical andes however several localities seem to have retained wetter conditions increasing the contrast between highly productive environments and the generally dry landscape this paper is only a first step towards a full understanding of the diversity and complexity of the mid holocene in different space time scales but a necessary one in order to start to model the resources structure available for human groups in the past in the andes

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

rheology of petrolatum paraffin oil mixtures applications to analogue modelling of geological processes abstract paraffins have been widely used in analogue modelling of geological processes petrolatum and paraffin oil are commonly used to lubricate model boundaries and to simulate weak layers in this paper we present rheological tests of petrolatum paraffin oil and several homogeneous mixtures of the two the results show that petrolatum and all petrolatum paraffin oil mixtures are strain strain rate and temperature dependent under typical experimental strain rates 10 3 10 1 s 1 for the same conditions pure paraffin oil is a slightly temperature dependent linear newtonian fluid all mixtures have yield stress and flow stress strain softening values that decrease with decreasing shear rate and with increasing relative amounts of paraffin oil the degree of strain rate dependence shear thinning also decreases with increasing paraffin oil content because these materials have rheologies that can be characterized and controlled they are suitable for use in a large number of analogue model settings either as a lubricant or to simulate weak layers when used as a lubricant mixtures with higher paraffin oil content should perform better than pure petrolatum

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

soilscape analysis at different scales using pattern indices in the jarama henares interfluve and henares river valley central spain abstract the jarama henares interfluve is located south of the ayllon range one of the easternmost ranges of the sistema central mountains in central spain the henares river valley is asymmetric with 20 topographic benches along its right bank and a series of glacis terraces on its left bank we investigated the soil geoform units in the jarama henares interfluve and the henares river valley using several indices to quantify and understand the evolution of soil and landscape patterns of the area during the plio quaternary features such fragmentation dominance geopedologic unit diversity relative spatial diversity size and shape neighbourhood and interaction were analysed in geopedologic maps prepared at two scales 1 18 000 and 1 50 000 using ancillary data aerial photographs and field observations likewise the taxonomic pedorichness and pedodiversity were assessed on plot maps at 1 100 scale representing three fluvial terrace areas of different age soil diversity analysis was carried out at the subgroup level of the usda soil taxonomy using 1 the number of individuals included in a given pedotaxum and 2 the areal proportion occupied by each soil taxum in a given map unit one of the main findings was that the values of the indices were higher and the number of indices required to describe appropriately the soilscape patterns was smaller at the local than at the regional scale the relative spatial diversity being one of the most useful indices at the plot scale taxonomic pedorichness and pedodiversity of soil subgroups increased from low young to high old terraces thus pattern indices can be used to characterise soilscape evolution aspects such as diversification due to the behaviour of the depositional system or to relief dissection

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia

environment and climate of the last 51 000 years new insights from the potrok aike maar lake sediment archive drilling project pasado in this introductory paper we summarize the history and achievements of the potrok aike maar lake sediment archive drilling project pasado an interdisciplinary project embedded in the international continental scientific drilling program icdp the stringent multiproxy approach adopted in this research combined with radiocarbon and luminescence dating provided the opportunity to synthesize a large body of hydrologically relevant data from laguna potrok aike southern patagonia argentina at this site lake level was high from 51 ka until the early holocene when the southern hemisphere westerlies shw were located further to the north at 9 3 ka cal bp the shw moved southward and over the latitude of the study area 52 degrees s causing a pronounced negative water balance with a lake level decrease of more than 50 m two millennia later the shw diminished in intensity and lake level rose to a subsequent maximum during the little ice age since the 20th century a strengthening of the shw increased the evaporative stress resulting in a more negative water balance a comparison of our data with other hydrological fluctuations at a regional scale in south eastern patagonia provides new insights and also calls for better chronologies and high resolution records of climate variability

new insights into paleoenvironmental changes in laguna potrok aike southern patagonia since the late pleistocene the pasado multiproxy record a series of long sediment cores was retrieved from laguna potrok aike southern patagonia within the framework of pasado potrok aike maar lake sediment archive drilling project an icdp interna