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

nature of the lithosphere across the variscan orogen of sw iberia dense wide angle seismic reflection data 1 two wide angle seismic transects have been acquired across the sw iberian massif they crossed three major geological zones south portuguese zone ossa morena zone and central iberian zone with their tectonic contacts and the pyrite belt being of greatest interest a total of 690 digital seismic recording instruments 650 texans and 40 reftek 3 component units from the iris passcal instrument pool were used the transects a and b are each approximately 300 km long and consist of 3 and 6 shot points respectively with an approximately 60 km shot point interval the charge sizes range from 1000 kg at the edges to 500 kg at the center these recently acquired experiments were designed to provide velocity constraints on the lithosphere and to complement the previously acquired normal incidence seismic profile iberseis both data sets are part of the sw iberia project which was developed within the europrobe program and designed to address fundamental questions about the nature and dynamics of the variscan lithosphere the acquisition parameters provide closely spaced wide angle seismic images of the lithosphere beneath sw iberia in transect a the station spacing was on average 400 m while along transect b the receiver spacing was approximately 150 m because of this close trace spacing the lateral continuity of the seismic arrivals is greatly improved frequency analysis revealed that the recorded events feature relatively low frequencies 6 25 hz after processing the shot records show high amplitude and well defined arrivals the interpreted pmp arrival located at approximately 11 s normal incidence traveltime is characterized by high amplitude and relatively low frequency 6 12 hz a well defined pn arrival appears at offsets beyond 120 km at far offsets greater than 180 km an upper mantle reflection is observed furthermore within the upper crust the shots records feature a relatively high velocity arrival located at 4 5 s normal incidence traveltime the analysis of this arrival indicates that it probably corresponds to the top of the iberian reflective body identified in the iberseis deep seismic profile the velocity models obtained by forward modeling show a complex crust especially in the middle crust the velocity models are the most detailed ones that have been produced in the area and contain a large amount of new features that are relevant to the understanding of the composition of the crust and upper mantle beneath the zone the velocity depth functions derived from the velocity models have higher middle crustal velocities than the average in other continental areas a comparison between laboratory seismic velocity measurements and the velocities of the models was carried out in order to estimate the crustal and the upper mantle composition results indicate that the high middle crust velocities correspond to rocks of a mafic composition the combined data set reveals new aspects related to the lithospheric evolution of this transpressive orogen and allows us to attempt an interpretative cross section of the upper lithosphere in sw iberia

unraveling middle crust conductive layers in paleozoic orogens through 3d modeling of magnetotelluric data the ossa morena zone case study sw iberian variscides 1 in recent years a number of magnetotelluric mt surveys have been carried out in the southern branch of the iberian variscan massif namely in the ossa morena zone omz and its neighboring areas the south portuguese zone spz and the central iberian zone ciz in order to determine the geoelectrical structure of this transpressive orogen and gain insight into its internal architecture new mt data collected across the omz complete a dense database that covers the whole belt and its boundaries this paper presents an integrative three dimensional model of the available mt data from the apparent resistivities four components impedance phases and geomagnetic transfer functions from 61 stations given the location of the study area near the atlantic ocean coast effect on the data was analyzed as well as the stability of the mesh due to the strong resistivity contrasts a mesh of 80 77 76 cells was finally used with an average cell size of 4 4 km in the horizontal direction and increasing thickness in the vertical direction from 25 m in the shallower layers to 5 km in the deepest ones the most striking feature is in addition to the conductive anomalies associated with the sutures between the spz omz and the omz ciz a conductive layer which spans the whole ossa morena middle to lower crust the top of this conductive layer is interpreted as a major decollement between the granulitic basement and the overlying meta sedimentary pile

asynchronous variation in the east asian winter monsoon during the holocene the east asian winter monsoon eawm is one of the most active components of the global climate system climate anomalies associated with the eawm differ between extratropical and tropical regions due to the eawm s meridional extent spatial differences in the eawm variability on centennial and millennial time scales during the holocene have not been well understood this study describes holocene spatiotemporal features of the eawm based on comparisons of proxy records and climate simulations the analysis specifically compared four proxy records located throughout china to assess the eawm s spatial variability during the holocene these records indicate a stronger eawm during the early holocene than that during the late holocene the eawm also shows a rapid asynchronous decline from northwestern to southeastern china the eawm declined in northwestern china from 10 to 7 5 ka b p whereas the decline did not occur in southern china and the eastern tibetan plateau until 6 4 5 ka b p coupled equilibrium and transient simulations of climate evolution during the holocene indicate that the decline of the eawm from 10 to 7 5 ka b p was probably caused by melting of northern hemisphere nh ice sheets and enhanced atlantic meridional overturning circulation amoc the decline of the eawm from 6 to 4 5 ka b p over the eastern tibetan plateau and southern china is related to an abrupt increase in sea surface temperatures ssts of the tropical western indian ocean we therefore argue that the regional shift in eawm intensity was probably related to a distinguishing response to high latitude nh ice sheets and amoc and low latitude tropical ssts forcings

constraints on the frontal crustal structure of a continental collision from an integrated geophysical research the central western betic cordillera sw spain 1 melange rocks outcrop widely in the central and western frontal sectors of the betic cordillera as in many other collisional orogens where they form part of the accretionary wedges extrusion of triassic plastic clays and evaporites was favored by the progressive accretion of the betic external zones mixing rocks of different provenance and forming a synorogenic frontal melange unit mt data coupled with gravity data are a valid combined methodology to characterize the geometry of these melange units since the characterization of plastic rocks geometry is usually uncertain using seismic techniques the results correlate well with known geological features sedimentary basins calcareous ranges evaporitic rocks and reveal the deep geometry a resistive body slightly dipping toward the se points to the continuity of the iberian massif below the guadalquivir basin 2 and the external zones 6 8 to the south gravity models show the iberian continental crust subducting below the internal zones with a roughly 20 35 slope the main conductive bodies are related to the location of evaporitic rocks involved in the frontal melange they overlie the iberian massif and southwards the frontal jurassic and cretaceous limestone sequences of the external and median subbetics in this setting thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction and being progressively accreted toward a frontal melange

sediments or soils multi scale geoarchaeological investigations of stratigraphy and early cultivation practices at kuk swamp highlands of papua new guinea abstract kuk swamp is a globally significant archaeological site of early agriculture in the highlands of papua new guinea mixed method and multi scalar investigations of the stratigraphy and selected feature fills at kuk were instrumental in determining the character of plant exploitation and agricultural practices there during the early and mid holocene in this paper macro scale field recording meso scale x radiography and micro scale thin section micromorphology analyses are presented in summary form for a stratigraphic column as well as for a palaeochannel and palaeosurfaces associated with plant exploitation at c 10 000 cal bp and cultivation at 7000 6400 cal bp major and minor stratigraphic units have been characterised primary and secondary formation processes differentiated and the anthropic associations of specific stratigraphic units determined especially in regards to cultivation the kuk research highlights several methodological problems with the investigation of early cultivation on allophane rich soils in tropical environments

are some of the deep crustal conductive features found in sw iberia caused by graphite abstract recent results obtained from two dimensional inversion of magnetotelluric mt data acquired in sw iberia reveal high conductive features at the middle lower levels of the crust the top of these anomalous structures correlates very well with the depth 10 13 km of an important seismic interface that has been interpreted as a regional detachment horizon very shallow and relatively narrow conductors in the ossa morena zone appear to correspond to small scale fluid deposited graphite systems in the preorogenic metasedimentary sequences some of the midcrustal conductors can be ascribed to graphite bearing thrust zones the formation of graphite with variable crystallinity being a consequence of variscan shearing processes deep seated conductors are tentatively interpreted as a result of relatively continuous highly crystalline grain boundary graphite films presumably preserved in basement granulite rocks assuming that graphite occurs as interconnected films calculations indicate that a fraction of 0 006 0 02 of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of mt models the role of graphite on the thermal behaviour of the crust is also discussed the results show that low contents of graphite do not significantly change the thermal behaviour of earth materials

geophysical model of the lithosphere across the variscan belt of sw iberia multidisciplinary assessment abstract a multidisciplinary geophysical study along a large seismic transect in the sw iberian peninsula has been carried out this study integrates the crustal structure geometry and composition obtained from normal incidence and wide angle seismic reflection data with other observables geoid gravity and topography the internal architecture of the lithosphere across the variscan orogen of sw iberia is constrained by the 300 km long high resolution deep normal seismic reflection iberseis transect the most prominent feature imaged by the seismic survey is the iberseis reflective body irb a 140 km long high amplitude reflective body located in the middle crust of the northern half of the transect the seismic velocity vp distribution within the crust and the upper mantle is constrained by two wide angle seismic transects acquired in the same area the velocity models show a complex crust with a specially complex middle crust which features higher velocities than the average continental crust also the wide angle data revealed that the irb is characterized by high velocities this feature was then interpreted as sill like structure built up by a series of mafic intrusions therefore a key issue is to study if this relatively mafic crust is consistent with other geophysical observables based on the velocity models two lithospheric density models have been derived along the iberseis wide angle transects the geoid gravity and topography response of these models have been calculated using a finite elements code that solves simultaneously the geopotential lithostatic and heat flow equations the resulting values are then compared with the measured observables and the crustal and lithospheric mantle geometry and density is modified until the best fit is obtained the initial density models calculated from the seismic data adjust quite well to the real potential field data however minor modifications have been required in order to properly fit the observables the final density models are consistent with the existence of relatively high density bodies in the mid crust providing further support to the seismic interpretation in addition they place new constraints on the location of the lithosphere asthenosphere boundary and on the tectonic evolution of sw iberia

crustal seismic structure beneath portugal and southern galicia western iberia and the role of variscan inheritance abstract the crustal structure in western iberia is the result of a complex geodynamic history most of the surface is covered by rocks dating to the variscan orogeny the coastal ranges dominated by mesozoic structures and mesocenozoic basins covering partially the mainland in this study we present the results of a local earthquake tomographic study performed to image in depth this complex crustal structure down to 24 km depth the obtained tomograms present a good correlation with the surface geology in general with higher vp velocities in the north and lower vp velocities in the south the heterogeneity observed on the surface geology of the galicia tras os montes zone is well marked being a relatively thin layer over the smoother structure of the centro iberia zone ciz the ciz crustal block confined between the porto tomar ferreira do alentejo and the manteigas braganca faults having higher vp values enhancing the contrast to the lusitanian basin to the west the ossa morena zone corresponds to the unit presenting the greater heterogeneity in both vp and vp vs models showing also with a complex transition to the south portuguese zone and a relatively smooth transition to the centro iberian zone unexpectedly the south portuguese zone present an east west velocity variation with no apparent correspondence with the surface geology the transition to the coastal mesocenozoic basins is clearly marked the lower tagus valley corresponding to a 4 km thick low velocity region the relocation inland recorded seismicity in the period 2000 2014 allows cleansing some of the alignments and establish their correlation with some of the active structures in portugal the model features and seismicity pattern reveal the strong role played by the variscan heritage

revealing the electrical properties of a gneiss dome using three dimensional magnetotellurics burial and exhumation cycles associated with faulting in central anatolia turkey abstract the nigde massif is a small scale exhumed lithospheric entity in central anatolia formed as a result of metamorphism driven by crustal thickening and migmatization its thermal and structural history records two burial and unroofing episodes induced by oblique tectonics related to an adjacent wrench zone of the ecemis fault to show the complex tectonic history of the events of this area its electrical resistivity structure was determined using three dimensional magnetotellurics forty seven high quality soundings within a frequency range of 320 hz 5000 s were utilized for this purpose the dimensionality of the data was investigated via phase tensor analyses and induction vectors a hydrothermal system that might be related to mt hasan was delineated as a widespread conductive zone in addition interpretation of the electrical resistivity models found a rheology seismicity relationship in the study area the nigde massif was depicted as a highly resistive dome like anomaly bounded by low angle detachment faults as indicated by the resistivity contrast between the massif and the adjacent features the lower boundary of the massif is defined by a resistive to conductive transition situated at 25 30 km depth beneath this transition a widespread low resistivity zone was interpreted as a partially melting lower crust this crustal feature is connected to a shallower anomaly beneath the ecemis fault zone which may infer the ascension of fluids that may be contributing to earthquake generation seismicity along the ecemis fault is overtly heterogeneous in that it tends to form a step approaching south along the fault where the lower crustal conductor is absent relevance between the seismicity and resistivity pattern denotes the presence of a fault configuration that is necessary for the yo yo tectonics

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

the palaeoenvironments of kuk swamp from the beginnings of agriculture in the highlands of papua new guinea pollen phytolith and charcoal records from the archaeological wetland site of kuk swamp wahgi valley papua new guinea spanning the period from 20 000 to 270 cal bp are compiled to reconstruct past vegetation and plant exploitation during the earliest to late phases of agricultural development samples collected from exposed stratigraphic sections associated with archaeological excavations enable detailed reconstructions of local vegetation and fire histories that can be directly linked to archaeological evidence for agricultural activity the record of past environmental change is constructed through detailed chronological control and stratigraphic correlation across the swamp revealing evidence of early holocene vegetation disturbance including short term patchy forest loss and burning considered indicative of plant exploitation it is not until the mid holocene after 7000 cal bp that persistent and widespread forest loss occurs with burning and the transplanting of musa banana into an open grassland environment which is contemporary with local archaeological features representing cultivation practices multi proxy palaeoecological evidence at kuk provides a robust vegetation history and land use chronology for the upper wahgi valley for the late pleistocene and holocene including the emergence of an agricultural landscape by 7000 cal bp subsequent agricultural developments in the highlands of new guinea can be seen as a series of continuing indigenous innovations in agricultural technology in the face of increased land degradation climate change and external influences

a comparison of three methods for the extraction of phytoliths from sediments abstract this paper compares three methods commonly used to extract fossil phytoliths from sediments a basic procedure using heavy liquid flotation and oxidation is compared with two other procedures across a range of sediment types commonly encountered in archaeological studies the three procedures are 1 a heavy liquid flotation method hlf 2 a burning method pow and 3 another heavy liquid flotation method hlfpol similar to hlf but adapted to allow the extraction of pollen and spores as well as phytoliths within a single process comparisons of the resulting output using these three techniques for phytolith extraction show that different methods can produce different results and therefore basic techniques should be modified according to the characteristics of the sediments for which they are used while all the techniques showed similarities in assemblage results there were problems associated with disaggregation and effective separation of light and heavy fractions in particular with the pow procedure the evidence suggests that morphotype selection occurred both within the physical sorting process and in the process of inverting slides to shed excess residue in both cases it is difficult to suggest a solution to the problem the results show clearly that the advantages gained by using the pow procedure are largely outweighed by the problems encountered with its use and because of possible size shape selection it is not recommended for general extraction procedures the heavy liquid flotation procedures on the other hand are shown to produce more concentrated residues with higher levels of clarity and less potential than the pow procedure for sample bias the use of a non toxic heavy liquid sodium polytungstate now allows the process to be used in relative safety it is recommended that analysts use heavy liquid flotation procedures with chemical treatments specific to sediment requirements

a late holocene palaeoecological record from ambra crater in the highlands of papua new guinea and implications for agricultural history a series of monoliths collected from ambra crater in the upper wahgi valley papua new guinea have been subject to multiproxy pollen microcharcoal and diatom palaeoecological investigation the palaeoecological record enables a relatively high resolution reconstruction from c 4000 500 cal bp throughout the sequence the valley floor and crater area were continuously deforested and carpeted with a grassland disturbance taxa mosaic vegetation communities in the valley were largely unaffected by successive tephra deposition events although some muted effects occurred tephra deposition did have considerable local effects on soil water conditions and hydrology in the base of the crater the ambra crater record is consistent with longer chronologies from wetlands in the upper wahgi valley which document extensive disturbance to dryland forests and their replacement with grasses and other disturbance taxa from the mid holocene the ambra crater record taken in conjunction with previously published multisite data enables critique and dis crimination of different interpretations of agricultural history in the highlands during the late holocene

the association between stratospheric weak polar vortex events and cold air outbreaks in the northern hemisphere previous studies have identified an association between temperature anomalies in the northern hemisphere and the strength of stratospheric polar westerlies large regions in northern asia europe and north america have been found to cool during the mature and late stages of weak vortex events in the stratosphere a substantial part of the temperature changes are associated with changes in the northern annular mode nam and north atlantic oscillation nao pressure patterns in the troposphere the apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting but only if the temporal and spatial nature of the coupling is known using 51 winters of re analysis data we show that the development of the lower tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well defined stages including the formation of geographically distinct cold air outbreaks at the inception of weak vortex events a precursor signal in the form of a strong high pressure anomaly over northwest eurasia is associated with long lived and robust cold anomalies over asia and europe a few weeks later near the mature stage of the weak vortex events a shorter lived cold anomaly emerges off the east coast of north america the probability of cold air outbreaks increases by more than 50 in one or more of these regions during all phases of the weak vortex events this shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks as large changes in the frequency of extremes are involved this process is important for the medium range and seasonal prediction of extreme cold winter days three hundred year pre industrial control simulations by 13 coupled climate models corroborate our results copyright 2010 royal meteorological society and crown copyright

magnetotelluric measurements in sw iberia new data for the variscan crustal structures 1 thirty new mt soundings were carried out in sw iberia allowing the investigation of the lateral continuity of some major structures and lithological features that are believed to control decisively the deep architecture of the ossa morena zone belts results of the two dimensional inversion of the data reveal high conductivity zones in the middle lower crust interpreted as the signal of a granulitic basement with grain boundary interconnected films of graphite the resistive features located preferentially in the upper middle crust are ascribable to igneous complexes of variable age

magnetotelluric survey of the electrical conductivity of the crust across the ossa morena zone and south portuguese zone suture abstract the transition between the south portuguese zone spz and the ossa morena zone omz is made up of a major geosuture which is indicated by the beja acebuches ophiolite several geological data suggest that this suture is the result of an oblique collision with a northward propagation between the spz and omz from the structural point of view the omz is much more complex than the adjacent central iberian zone and the spz the frequently complicated internal structure is the result of superposition of various structural elements developed during different tectonic events with the aim of providing new constraints to this complex deep structure a magnetotelluric mt survey was designed by the universities of lisbon and barcelona in the scope of the bilateral cooperation and the europrobe programs a first nne ssw profile across the spz and omz was carried out in september 1997 the profile is 40 km long and consists of nine deep mt soundings with periods ranging from 0 0039 to 4000 s the time series were processed using a robust algorithm after visual inspection the study of the dimensionality and directionality of the regional electrical structures is based on the analysis of the induction arrows and the groom bailey decomposition a strike of n125e was determined in accordance with regional geological features 2 d inversion was undertaken on both te and tm modes using the rri method the main feature of the model is a large conductive body

natural and human impacts in a 35 000 year vegetation history in central new britain papua new guinea abstract phytoliths and micro charcoal from the yombon airstrip archaeological site in central new britain papua new guinea provide the longest vegetation history record yet available for the new guinea islands the record begins about 35 kya with the first evidence for human presence at the site and with the exception of the last glacial maximum period is continuous to the present three other sites provide supplementary evidence including plant macro remains from the early holocene onwards the record is punctuated by a series of volcanic events which are reflected in the vegetation record by alternating frequencies of closed forest and regrowth elements micro charcoal is present from the oldest levels and fluctuates in frequency throughout the sequence increasing substantially from the terminal pleistocene early holocene onwards this coincides with the first appearance of panicoid grasses and a range of potential cultivars including bananas and saccharum increased levels of burning coinciding with the appearance of potential plant cultivars may indicate shifts in plant food production leading to cultivation from the early holocene onwards this compares favourably with previously reported evidence from garua island off the north coast of new britain the combination of trends in burning vegetation clearance and appearance of potential cultivars on new britain appears to parallel changes in the papua new guinea highlands at a similar time and suggests regional similarities in subsistence and vegetation management practices from before the lgm onwards further studies are needed to clarify the timing and extent of these shifts across the region and to provide a vegetation picture for the period before human colonisation of new britain

transcurrent continental tectonics model for the ossa morena zone neoproterozoic paleozoic evolution sw iberian massif portugal the ossa morena zone sw iberian massif was affected by continuous orogen parallel transcurrent continental tectonics from the neoproterozoic to the carboniferous times involving transtension tt and transpression tp processes that co existed together occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically a first stage of transpression tp1 took place during the late neoproterozoic lower cambrian as a result of cadomian arc continent collisional processes structures generated by transtension tt1 from cambrian to lower devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments tilting rifting and important tectono thermal diachronic processes denudation phenomena and inhibition of sedimentation related with thermal uplift asthenosphere upwelling and consequent subsidence caused by isostatic equilibrium involving generalized transgressions were processes responsible for major unconformities the variscan tp2 tt2 episodes that followed diachronically tp1 tt1 by maintaining the orogen parallel transport direction were concomitant with syntectonic deposition of continental basins in the omz and foreland basins in the spz tt2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones favoured the opening of tectonic troughs filled up by sediments and volcanism tp2 shortening have generated fold axes parallel to the orogen strike and composite dissymmetric flower structures

palynomorph evidence for tropical climate stability in the gulf of papua papua new guinea over the latest marine transgression and highstand 14 500 years bp to today abstract three sediment cores mv 41 mv 46 and md 50 from the gulf of papua gop papua new guinea were analyzed to assess changes in climatic oceanographic and sedimentological conditions over the last 14 5 kyr palynomorphs which were isolated from sediment core samples were collected at approximately 0 5 m intervals using a strong acid and oxidant md 50 non oxidant mv 41 mv 46 procedure radiocarbon 14c stable isotope geochronology magnetic susceptibility stable isotope analysis md 50 only oxygen 18 18o and carbon 13 13c and clay mineral maturity analysis were also completed for each core palynological data indicate that climatic conditions at sea level have remained warm wet and stable for the past 14 5 kyr with sea surface temperatures in the gop above 14 c potential decreases in vegetative cover marked the younger dryas interval 12 5 11 5 kyr bp as indicated by reduced pollen and spore recovery the end of the latest marine transgression and the subsequent return to eustatic sea level highstand is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr bp an increase in seasonality and potential el nino southern oscillation variability is observed in md 50 s oxygen isotope results at 5 kyr bp this is not supported by the palynomorph record likely because of the sampling interval and dilution by tropical pollen flora which indicates stable climatic conditions throughout the last 14 5 kyr sediment transport pathways in the gop remained fairly constant throughout the time interval which is supported by the lack of major changes in palynomorph assemblage composition

electromagnetic imaging of variscan crustal structures in sw iberia the role of interconnected graphite abstract the western part of the iberian peninsula iberian massif is the best exposed fragment of the variscan orogen in europe its southern half was generated by an oblique collision between three continental terranes belonging to the margins of laurassia avalonia the south portuguese zone spz and gondwana the ossa morena zone omz and the central iberian zone ciz the boundaries between them are considered to be suture zones a 200 km long magnetotelluric profile across the three variscan terranes was done in a nne direction approximately perpendicular to the main tectonic features the results of two dimensional inversion of the mt dataset reveal high conductivity zones coinciding with the transitions spz omz and omz ciz these conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime a high conductivity layer extending along the whole omz was found at a depth of 15 25 km the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile the high conductivity was interpreted as caused by the precambrian serie negra graphite rich rocks carbon and oxygen x ray mapping with electron microprobe on polished sections of serie negra samples from omz revealed the presence of interconnected graphite which supports the hypothesis that graphite is determinant for the high conductivity two graphite types which help to record the geological evolution were identified graphite accumulations in the schistosity surfaces produced by folding and metamorphism and metallic films of graphite developed along late faults the conductive layer shows blobs of higher conductivity suggesting macro anisotropy additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity given that the detachment level is located within the serie negra several high resistivity features were found in the upper crust related to devonian and carboniferous successions and probably to some unexposed plutons in the spz and the palaeozoic series of omz plus some granitic intrusions in the ciz a high resistivity zone extending to the whole crust is correlated with extensive late variscan granite intrusions

late quaternary vegetation change in the tari basin papua new guinea the changes in late quaternary vegetation at two sites in the tari basin central highlands of new guinea are presented haeapugua basin 1650 m altitude and tugupugua basin 2300 m altitude lie within the lower montane forest belt where the climate is characterised by high relative humidity and low seasonality pollen analysis mineral magnetics carbonised particle analysis and dating by radiocarbon and thermoluminescence techniques are employed to reconstruct the vegetation and sediment history the sequences include fragmentary interglacial interstadial records from before 50 000 yr b p and a continuous record from at least 28 000 yr b p to the present the study shows that prior to 21 000 yr b p vegetation in the basin was dominated by fluctuating proportions of tree taxa indicative of a forested environment the montane forest taxon nothofagus is important throughout the record although other tree taxa including castanopsis myrtaceae dacrydium and pandanus attain dominance at different times under the influence of a range of environmental factors the creation of an open environment around 21 000 yr b p is considered to be a consequence of the arrival of humans in the region the late glacial transition between 14 500 and 8500 yr b p is a period of climatic instability with landscape and vegetation adjustments proceeding at different rates across the highlands vegetational adjustments match modern ranges by about 8500 yr b p when swamp forest developed across the sites at the lower altitude site there are indications of anthropogenic forest disturbance associated with swamp forest clearance commencing around 1700 yr b p and intensifying through to the present forest clearance is recorded only after 700 yr b p at the higher site where agriculture was probably only sustainable after the introduction of sweet potato ipomoea batatas

a first look at oxygen isotope records from modern and holocene aged gastropod stenomelania shells from lake kutubu papua new guinea the lake kutubu project was funded by the department of archaeology and natural history at the anu and the australian institute of nuclear science and engineering ainse grants aingra08028 and aingra10113 obtained by s g h

constraints on the crustal structure of the internal variscan belt in sw europe a magnetotelluric transect along the eastern part of central iberian zone iberian massif 1 the iberian massif is the best exposed segment of the european variscan belt it includes relatively well preserved terranes that were accreted by transpression along time and resulted in a number of geotectonic units that formed part of the late paleozoic assembly of the pangaea supercontinent in sw iberia these units are the central iberian zone ciz ossa morena zone omz and the south portuguese zone spz a 210 km long ne sw magnetotelluric profile was carried out through the ciz from the omz ciz boundary toward the north reaching the tagus cenozoic basin data dimensionality analysis resulted in a suitable 2 d electrical resistivity structure allowing a 2 d inversion of the data set complementary available geophysical data deep seismic gravity and aeromagnetic and a comparison with a detailed geological cross section led us to constrain the interpretation of the 2 d electrical resistivity structure of the ciz crust the results show for the upper crust the existence of diverse conductive resistive bodies that correlate well with known geological features sedimentary basins faults granitic plutons mineralized systems a mild but steady conductive band is located along the middle and lower crust that is interpreted as a mafic granulite basement the upper section of this band connects with several elongated shallow conductors providing further evidence for the existence in the central iberian zone of a complex decollement system where the major faults are rooted such a crustal architecture is viewed as the northward continuation of the variscan large scale structures previously recognized in the southern sectors omz and spz

crustal structure of an intraplate thrust belt the iberian chain revealed by wide angle seismic magnetotelluric soundings and gravity data abstract the iberian chain is a cenozoic intraplate thrust belt located within the iberian plate unlike other belts in the iberia peninsula the scarcity of geophysical studies in this area results in a number of unknowns about its crustal structure the iberian chain crust was investigated by means of a ne sw refraction wide angle reflection seismic transect and two magnetotelluric profiles across the chain oriented along the same direction the seismic profile was designed to sample the crust by means of three shots designed to obtain a reversed profile the resulting velocity depth model shows a moderate thickening of the crust toward the central part of the profile where crustal thickness reaches values above 40 km thinning toward de sw tajo and ne ebro foreland basins the crustal thickening is concentrated in the upper crust the seismic results are in overall agreement with regional trends of bouguer gravity anomaly and the main features of the seismic model were reproduced by gravity modeling the magnetotelluric data consist of 39 sites grouped into two profiles with periods ranging from 0 01 s to 1000 s dimensionality analyses show significant 3d effects in the resistivity structure and therefore we carried out a joint 3d inversion of the full impedance tensor and magnetic transfer functions the mesozoic and cenozoic basins along the chain are well characterized by shallow high conductive zones and low velocities elongated conductors reaching mid crustal depths evidence the presence of major faults dominating the crustal structure the results from the interpretation of these complementary geophysical data sets provided the first images of the crustal structure of the iberian chain they are consistent with a cenozoic shortening responsible of the upper crust thickening as well as of the uplift of the iberian chain and the generation of its present day topography

confidence intervals for age estimates and deposition times in late quaternary sediment sequences distribution sampling from sequences of radiocarbon ages is used to obtain confidence intervals for intermediate age estimates sediment deposition times and thence pollen deposition rates three

electromagnetic imaging of a transpressional tectonics in sw iberia forty one magnetotelluric soundings were carried out along a 200 km long profile approximately nne ssw across the three major geotectonic units in sw iberia a model obtained from two dimensional inversion of the magnetotelluric data set reveals high conductivity zones in the middle lower crust 10 30 km two of these zones correspond to the transition between the main geotectonic units one between the south portuguese zone and the ossa morena zone interpreted as having been caused by metasediments and the other between the ossa morena zone and the central iberia zone associated with a shear zone and metasediments another high conductivity anomaly related to black shales with major graphite impregnation was detected within the ossa morena zone the resistive features located preferentially in the upper crust 1 10 km coincide with gabbroic and granitic complexes

evidence of a large deep conductive body within the basement of the guadalquivir foreland basin betic cordillera s spain from tipper vector modelling tectonic implications abstract the betic cordillera is an alpine belt formed by the interaction of the eurasian and african plates and the westward motion of the alboran domain long period magnetotelluric observations at 26 sites in its westernmost part provide induction arrows that have been compared with 3d forward models including bathymetry and major geological bodies the results highlight the presence of a major conductive body 0 05 m unknown to date and located within the basement of the guadalquivir foreland basin aeromagnetic and field magnetic measurements further support the occurrence of magnetic anomalies related to the top of this anomalous body this major structure is interpreted as an intermediate or basic igneous rock with a high proportion of metallic mineralization its origin is discussed in the framework of the regional geological setting possibly produced in the southern iberian variscan massif by a huge concentration of volcanogenic massive sulphide vms in the prolongation of the iberian pyrite belt during devonian early carboniferous times another possibility is that the conductive anomaly is due to magmatic intrusions associated with the mesozoic fragmentation of southern iberia and the opening of the tethys

3 d electromagnetic imaging of a palaeozoic plate tectonic boundary segment in sw iberian variscides s alentejo portugal abstract in sw iberian variscides the boundary between the south portuguese zone spz and the ossa morena zone omz corresponds to a major tectonic suture that includes the beja acebuches ophiolite complex baoc and the pulo do lobo antiform terrane plat three sub parallel and approximately equidistant mt profiles were performed covering a critical area of this palaeozoic plate tectonic boundary in portugal the profiles running roughly along an ne sw direction are sub perpendicular to the main variscan tectonic features results of the three dimensional 3 d modelling of mt data allow to generate for the first time a 3 d electromagnetic imaging of the omz spz boundary which reveals different conductive and resistive domains that display morphological variations in depth and are intersected by two major sub vertical corridors these corridors coincide roughly with the ne sw messejana strike slip fault zone and with the wnw ese ferreira ficalho thrust fault zone the distribution of the shallow resistive domains is consistent with the lithological and structural features observed and mapped integrating the expected electrical features produced by igneous intrusions and metamorphic sequences of variable nature and age the development in depth of these resistive domains suggests that 1 a significant vertical displacement along an early tectonic structure subsequently re taken by the messejana fault zone in late variscan times has to be considered to explain differences in deepness of the base of the precambrian cambrian metamorphic pile 2 hidden syn to late collision igneous bodies intrude the meta sedimentary sequences of plat 3 the roots of baoc are inferred from 12 km depth onwards forming a moderate resistive band located between two middle crust conductive layers extended to the north in omz and to the south in spz these conductive layers overlap the iberian reflective body evidenced by the available seismic reflection data and are interpreted as part of an important middle crust decollement developed immediately above or coinciding with the top of a graphite bearing granulitic basement

coral reef calcification and climate change the effect of ocean warming 1 coral reefs are constructed of calcium carbonate caco3 deposition of caco3 calcification by corals and other reef organisms is controlled by the saturation state of caco3 in seawater and sea surface temperature sst previous studies have neglected the effects of ocean warming in predicting future coral reef calcification rates in this study we take into account both these effects by combining empirical relationships between coral calcification rate and and sst with output from a climate model to predict changes in coral reef calcification rates our analysis suggests that annual average coral reef calcification rate will increase with future ocean warming and eventually exceed pre industrial rates by about 35 by 2100 our results suggest that present coral reef calcification rates are equivalent to levels in the late 19th century and does not support previous suggestions of large and potentially catastrophic decreases in the future