kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern mediterranean region since the late cretaceous the relationship between subduction dynamics and crustal deformation in the mediterranean region has been recently studied using three dimensional 3d numerical models such models require however a detailed information concerning the past geological evolution we use stratigraphic petrologic metamorphic structural paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern mediterranean region since the late cretaceous using the principle of non rigid domains the motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations the directions and amounts of displacement on crustal scale shear zones and the burial and exhumation histories of the main metamorphic units extracted from these reconstructions paleotectonic maps and lithospheric scale cross sections illustrate that the present day subduction zone has been continuously retreating southward since the late cretaceous and has accreted several small continental domains in the process we find evidence for two back arc related extensional events 1 slow extension along the balkans and the pontides in the late cretaceous while the trench was long and linear and 2 faster extension in the rhodope aegean west anatolian region since the eocene oligocene rapid rotation of the hellenides between 15 and 8 ma probably indicates a slab tearing event below western anatolia that could have further accelerated this extensional kinematics spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation

late quaternary fluvial terrace evolution in the main southern amazonian tributary abstract late quaternary sedimentary deposits from amazonian lowlands are important geological archives for understanding the origin evolution and controls of the largest fluvial drainage basin on earth climate has been most often claimed as the main factor affecting river evolution in this region an increasing volume of publications have also highlighted tectonics as a relevant control this work investigates the late quaternary evolution of the madeira river the biggest southern tributary of the amazonas basin and a major waterway in south america with the goal of discussing the factor with highest potential of influence on its development in space and time the approach consisted of carrying out a detailed morphological sedimentological and chronological characterization of terrace deposits three terraces were recognized which record sandy pebbly channel muddy channel oxbow lake point bar floodplain as well as crevasse channel crevasse splay and levee deposits the topographically highest terrace t1 formed in the time interval before 43 500 and 31 696 32 913 cal yrs bp the intermediate terrace t2 between 25 338 26 056 and 14 129 14 967 cal yrs bp and the lowest terrace t3 between 12 881 13 245 and 3158 3367 cal yrs bp these terraces are the testimony of successive downcutting and sediment aggradation episodes of terrace erosion and deposition cannot be fully accommodated within the framework of fluctuating river base level tied to late pleistocene holocene global or regional climate fluctuations changes in tectonic subsidence rates might have played an important role in the equilibrium state of this particular fluvial system

acid and basic late neogene volcanism in central aegean sea its nature and geotectonic significance local eruptions of acid volcanic rocks occurred in the central aegean region around the miocene pliocene boundary rhyolites outcrop on the island of antiparos located in the central part of the attic cycladic massif the age of these volcanic rocks ranges from 4 0 to 5 4 m y and chemical and sr isotopic data suggest they were generated by partial melting of the continental crust at the same time along the border of the attic cycladic massif i e on the island of patmos and caloyeri local eruptions of naalkaline basalts occurred the whole of the eruptive activity is interpreted as an expression of the marked tensional tectonic phase which has affected the central aegean area since middle miocene the contrasting nature of the erupted volcanic rocks crustal and sub crustal is attributed to the different thermal state of the lithosphere beneath the two areas as emphasized also by the presence of a wide granitic belt of mainly miocene age which developed in the median sector of the attic cycladic massif

mapping of a major paleodrainage system in eastern libya using orbital imaging radar the kufrah river paillou p schuster m tooth s farr t rosenqvist a lopez s malezieux j m 2009 mapping of a major paleodrainage system in eastern libya using orbital imaging radar the kufrah river earth and planetary science letters 277 3 4 327 333 sponsorship french space agency cnes centre national d etudes spatiales

evolution of the lowest amazon basin modeled from the integration of geological and srtm topographic data morphologic features obtained from srtm data integrated with geologic information are emphasized in this paper in order to provide the basis for understanding the development of the lowest amazon drainage basin focusing on the history of one of the largest amazonian tributaries the tocantins river and on the origin of the marajo island throughout the quaternary this approach led to the recognition of a fan morphology related to the record of a tectonically controlled n nw s se orientated paleovalley cut down into miocene and older rocks the incised valley was fed by a paleo tocantins river which deposited its sediment load continuously to the north northwest reaching the marajo island and producing a deposit with a fan morphology during the plio pleistocene pleistocene as characterized in the srtm images this channel system became abandoned due to capture by ne sw orientated faults and establishment of the para river by w e strike slip movements this event which probably took place in the mid holocene was responsible for the detachment of the marajo island from the mainland 2006 published by elsevier b v

a mid late holocene tidally influenced drainage system revealed by integrated remote sensing sedimentological and stratigraphic data abstract despite the growing employment of remote sensing rs techniques in paleoenvironmental studies the stratigraphic interpretation of rs derived paleodrainage traces is still an open issue as their relation to subsurface is largely unexplored here we applied a multi data analysis approach including publicly available optical images from different satellites landsat aster sentinel hyperion lidar derived digital terrain model dtm soil reflectance spectra and facies core data which succeeded in revealing a paleodrainage system buried beneath a 200 sq km wide wetland the mezzano lowland ml of the po coastal plain northern adriatic sea italy data integration in a gis environment allowed the 3d mapping of numerous and temporally persistent meandering traces from distal to proximal locations the rs derived traces show a hierarchical organization in terms of sinuosity and width and form a dense and dendritic pattern typical of a tidally influenced system surface and subsurface cross investigation of two meandering traces through soil reflectance spectra and core stratigraphy reveal that these landforms represent the surface expression of buried channels that eroded the underlying lagoonal succession with lateral transition to intertidal deposits lidar detected micro morphologies related to paleomeanders evolution strongly influenced the spatial distribution of mid late holocene peat bearing lithofacies i e salt marsh and swamp and hence soil moisture distribution inducing the sharp radiance contrasts traces detected by satellite sensors on the surface on trace areas invariably lack peat deposits and record the top of 3 4 m thick channel fill sands some 2 4 m below the ground level in contrast out of trace areas are characterized by organic rich soils that cap a 2 5 3 5 m thick succession of intertidal supratidal peat deposits accumulated in depressed areas lateral to the channel levee complex we conclude that in the early stage of po delta construction between ca 6000 2500 cal yr bp two distinct tidal influenced drainage networks fed the mezzano lowland lagoon under a predominantly autogenic control these findings indicate the suitability of a low cost rs stratigraphic approach to improve the reconstruction of past paleogeographic scenarios buried beneath deltaic lowlands shedding new light on the evolution trends of coastal landforms environments and sedimentary patterns under highstand conditions

role of continental crust in petrogenesis of orogenic volcanic associations abstract orogenic volcanic rocks form a continuous spectrum between tholeiitic associations of island arcs and calc alkaline associations of continental margins and collision zones although these settings show a wide variation in plate convergence rate depth of scismic zone nature and age of subducted and over riding lithosphere the compositional characteristics of the volcanic association is correlated most strongly with crustal thickness tholeiitic associations dominated by basaltic rocks and with high feott mgo and low k2o for a given sio2 content are restricted to island arcs with crustal thickness less than 20 km more calc alkaline associations dominated by andesitic rocks with lower feot mgo and higher k2o for a given sio2 content occur in areas where crustal thickness exceeds 20 km these suggest that 1 fractional crystallization occurring within the continental crust may be the major mechanism responsible for variations within orogenic volcanic associations and 2 formation of calc alkaline associations may require the presence of continental crust these relationships suggest that calc alkaline magmas may be derived from more tholeiitic magmas by fractional crystallization possibly combined with crustal melting or contamination the extension of these processes might be responsible for formation of silicic ignimbrites occurring in continental areas where the crustal thickness exceeds 30 km in areas of crustal extension

paleomagnetic evidence for neogene rotational deformations in the aegean domain new paleomagnetic data are reported from the islands of skyros and lesbos in central aegea and the izmir foca region in western anatolia together with previous results obtained in northwestern greece and with results from northern aegea reported by others authors these data suggest that the lower miocene arc was almost rectilinear trending e w and that the curvature was acquired by opposed rotational deformations at each termination moreover the observed inclinations which are shallower than those expected on the basis of a geocentered dipole field suggest a large northward drift since middle miocene

erosion of an active fault scarp leads to drainage capture in the amazon region brazil far from the continental margin drainage basins in central amazonia should be in topographic steady state but they are not abandoned remnant fluvial valleys up to hundreds of square kilometers in size are observed throughout amazonia and are evidence of significant landscape reorganization while major late miocene drainage shifts occurred due to initiation of the transcontinental amazon river local landscape change has remained active until today driven either by dynamic topography tectonism and or climatic fluctuations drainage captures in amazonia provide a natural experiment for assessing the geomorphic response of low slope basins to sudden capture related base level falls this paper evaluates the timing of geomorphic change by examining a drainage capture event across the baependi fault scarp involving the cuieiras and taruma mirim river basins northwest of the city of manaus in brazil a system of capture related knickpoints was generated by base level fall following drainage capture through numerical modeling of their initiation and propagation the capture event is inferred to have occurred between the middle and late pleistocene consistent with other studies of landscape change in surrounding areas in low slope settings like the amazon river basin base level fall can increase erosion rates by more than an order of magnitude and moderate to large river basins can respond to episodes of base level fall over timescales of tens to hundreds of thousands of years copyright 2013 john wiley sons ltd

the thrace basin in the rhodope province of ne greece a tertiary supradetachment basin and its geodynamic implications abstract detailed tectonic analysis and geological mapping on the tertiary molassic and volcanosedimentary rocks of the thrace basin in northeastern greece allowed us to reconstruct the structural evolution of the basin and its geotectonic setting as well as the orientation of the regional paleostress field sedimentation was linked with a calc alkaline and locally shoshonitic magmatism associated with the tertiary syn to late orogenic extension in the rhodope province we interpret the molassic tertiary greek part of the thrace basin as a supradetachment basin associated with sedimentary and volcanic infilling five 5 deformational events t1 to t5 have been distinguished during basin evolution from eocene to quaternary time t1 is related to a low angle normal detachment fault zone with a top to the sw to ssw sense of movement and initial basin subsidence during middle late eocene to oligocene time simultaneously with uplift and exhumation of the footwall rhodope metamorphic rocks stacking and crustal thickening in the more external parts of the hellenic orogenic belt have taken place during the same time t2 evolved during oligocene miocene time it was characterized by transpressional tectonics and formation of large strike slip faults and extensional fractures as well as conjugate thrust faults and folds with n nw or s se sense of movement during miocene pliocene time the third t3 event took place it was responsible for the high angle normal faults dismembering the eocene oligocene molassic basin into neogene grabens the t4 event affected the neogene sediments of the basin with minor reverse strike slip faults as well as normal faults the following t5 event is related to large normal active faults they coincided with the active tectonics of the study area defined by the earthquake focal mechanisms

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

geomorphological approaches to the study of neotectonics the study of morphotectonics is concerned with the analysis of landforms whose form or origins have been affected by neotectonic activity traditional morphotectonic studies have been used as a basis for more refined e g statistical analyses after the 1960s however there emerged new techniques and new approaches to the study of morphotectonics these have made more precise not only the recognition of morphotectonic features but have also improved their dating the time has come to integrate morphotectonic studies more fully both with the approaches used by other disciplines and with modern geomorphological theory

south aegean volcanic arc geochemical variations and geotectonic implications the aegean volcanic arc is one of the most important geological structure of the mediterranean area it is a belt of volcanic centers consisting of products ranging from basaltic andesitic dacitic to rhyolitic in composition all of them displaying a typical calc alkaline chemical character

evolution of the holocene mississippi river floodplain ferriday louisiana insights on the origin of fine grained floodplains abstract the alluvial architecture and soil characteristics of holo cene mississippi river floodplain deposits in the southern lower mississippi valley provide evidence for significant changes in floodplain development in response to sea level rise floodplain cores acquired near ferriday louisiana show that holocene deposits consist of 15 30 m ave 20 m of sands silts and clays which overlie late wisconsin sands and gravels on the basis of differences in sediment grain size sediment body geometry and the abundance of soil features the holocene deposits are subdivided into lower and upper holocene units lower holocene deposits 5000 yr b p consist of lacustrine and poorly drained backswamp muds that contain authigenic siderite pyrite and vivianite and show little evidence of soil formation muds encase crevasse splay and floodplain channel sand bodies 1 km wide and collectively these deposits represent a mosaic of shallow lakes poorly drained backswamps and multichannel streams similar to modern examples in the atchafalaya basin 100 km south of ferriday upper holocene deposits 5000 yr b p are represented by large mississippi river meander belt sand bodies that are up to 15 km wide and 30 m thick natural levee silts and sands and well drained backswamp muds are present between meander belt sands upper holocene deposits contain abundant soil features and sandy and silty soils are entisols inceptisols and alfisols whereas clayey soils are vertisols the presence of isolated sand bodies surrounded by mud and the scarcity of soil features suggest that lower holocene sediments reflect a period of rapid floodplain aggradation during which crevassing lacustrine sedimentation and avulsion dominated floodplain construction no evidence of large meandering mississippi river channels represented by buried thick tabular sands exists near ferriday and discharge in lower mississippi valley flow was probably conveyed by a network of small multichannel floodplain streams upper holocene sediments record a dramatic change ca 5000 yr b p from rapid to slower floodplain aggradation which was accompanied by extensive lateral channel migration overbank deposition and soil formation on the basis of differences in meander belt dimensions and numbers of abandoned channels upper holocene meander belts are subdivided into simple and complex forms relative age relationships suggest that the smaller and older simple meander belts represent periods of divided mississippi river flow and early attempts to establish a large single channel meandering regime this type of meandering regime is represented by the larger and younger complex meander belts and includes the modern meander belt similarities in the timing of changes in floodplain processes and fluvial style and decreasing rates of holocene sediment accumulation in the southern lower mississippi valley strongly suggest that decelerating holocene sea level rise in the gulf of mexico affected floodplain development at least 300 km inland from the present day coast the alluvial architecture of the lower holocene deposits and the absence of large meandering mississippi river channel deposits older than 5000 yr b p near ferriday indicates that most of the floodplain muds were deposited by avulsion related crevassing and lacustrine sedimentation rather than by overbank flooding of large mississippi river channels similarities between the floodplain history of the mississippi river and those of modern and ancient rivers elsewhere further suggest that avulsion rather than simple overbank deposition contributes to the construction of fine grained floodplains to a greater degree than generally recognized

geomorphological evidence of recent tilting in the central amazonia region abstract geomorphometric techniques applied to remote sensing data represent powerful tools as an aid for detecting terrain features produced by recent vertical crustal movements in a variety of landscapes in this work geomorphometric analysis of the central amazonia drainage network using shuttle radar topography mission srtm data was carried out to determine surface water loading and tectonic influence on the development of the uatuma and urubu river basins since the miocene the main objective was to detect geomorphological domains of lateral stream migration and channel sinuosity changes that could indicate recent vertical crustal movement to achieve this the transverse topographic symmetry factor and sinuosity index were applied to analyze the study area drainage network comparison of the geomorphological domains with structural field data and records of seismicity suggests that they are influenced by subsurface fault reactivation which coincides in space with faults mapped in outcrops that have activated since the miocene this interpretation is corroborated by the spatial correspondence between these faults with domain boundaries and shapes by river sinuosity change when crossing these boundaries and by a high concentration of seismic activity along one of these limits the crustal movement caused by hydrological loading can also influence such geomorphological features such is the case of lateral stream migrations of a domain in the opposite sense to the amazon river flow this may be a consequence of the more pronounced expression of hydrological loading in the negro and solimoes river confluence region

palaeohydrology of the fazzan basin and surrounding regions the last 7 million years abstract we have integrated information on topography geology and geomorphology with the results of targeted fieldwork in order to develop a chronology for the development of lake megafazzan a giant lake that has periodically existed in the fazzan basin since the late miocene the development of the basin can be best understood by considering the main geological and geomorphological events that occurred thought libya during this period and thus an overview of the palaeohydrology of all libya is also presented the origin of the fazzan basin appears to lie in the late miocene at this time libya was dominated by two large rivers systems that flowed into the mediterranean sea the sahabi river draining central and eastern libya and the wadi nashu river draining much of western libya as the miocene progressed the region become increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked the river nashu in late miocene or early messinian times forming a sizeable closed basin in the fazzan within which proto lake megafazzan would have developed during humid periods the fall in base level associated with the messinian desiccation of the mediterranean sea promoted down cutting and extension of river systems throughout much of libya to the south of the proto fazzan basin the sahabi river tributary know as wadi barjuj appears to have expanded its headwaters westwards the channel now terminates at al haruj al aswad we interpret this as a suggestion that wadi barjuj was blocked by the progressive development of al haruj al aswad k ar dating of lava flows suggests that this occurred between 4 and 2 ma this event would have increased the size of the closed basin in the fazzan by about half producing a catchment close to its current size 350 000 km2 the fazzan basin contains a wealth of pleistocene to recent palaeolake sediment outcrops and shorelines dating of these features demonstrates evidence of lacustrine conditions during numerous interglacials spanning a period greater than 420 ka the middle to late pleistocene interglacials were humid enough to produce a giant lake of about 135 000 km2 that we have called lake megafazzan later lake phases were smaller the interglacials less humid developing lakes of a few thousand square kilometres in parallel with these palaeohydrological developments in the fazzan basin change was occurring in other parts of libya the lower pliocene sea level rise caused sediments to infill much of the messinian channel system as this was occurring subsidence in the al kufrah basin caused expansion of the al kufrah river system at the expense of the river sahabi by the pleistocene the al kufrah river dominated the palaeohydrology of eastern libya and had developed a very large inland delta in its northern reaches that exhibited a complex distributary channel network which at times fed substantial lakes in the sirt basin at this time libya was a veritable lake district during humid periods with about 10 of the country underwater

late quaternary sedimentary dynamics in western amazonia implications for the origin of open vegetation forest contrasts abstract this work investigated the evolution of sedimentary environments during the latest quaternary and their influence on the paradoxical occurrence of open vegetation patches in sharp contact with the amazonian forest the approach integrated pre existing geological and floristic data from lowlands in the brazilian amazonia with remote sensing imagery including multispectral optical images tm etm and aster phased array l band synthetic aperture radar palsar insar c band srtm dems and high resolution images obtained from google earth the detection of an abundance of paleomorphologies provided evidence of a scenario in which constant environmental shifts were linked to the evolution of fluvial and megafan depositional systems in all studied areas the open vegetation patches are not random but associated with sedimentary deposits representative of environments either deactivated during the holocene or presently in the process of deactivation sedimentary evolution would have determined the distribution of wetlands and terra firme in many areas of the amazonian lowlands and would have a major impact on the development of open vegetated patches within the modern rainforest subsiding areas were filled up with megafan deposits and many fluvial tributaries were rearranged on the landscape the close relationship between vegetation and the physical environment suggests that sedimentary history related to the evolution of depositional settings during the latest quaternary played a major role in the distribution of flooded and non flooded areas of the amazonian lowlands with a direct impact on the distribution of modern floristic patterns as the depositional sites were abandoned and their sedimentary deposits were exposed to the surface they became sites suitable for vegetation growth first of herbaceous species and then of forest although climate fluctuations might have been involved fault reactivation appears to have been the main cause of changes in depositional dynamics through time a process that had an immediate effect on the development of large open vegetation patches intermingled with the amazonian rainforest

late quaternary of the middle caqueta river area colombian amazonia the late quaternary history of the middle caqueta river area in colombia northwestern amazonia is described based on observations of river bank sections radiocarbon dates and palynological analyses of organic layers in floodplain and low terrace sediments of the caqueta river it is shown that the late pleistocene and holocene climatic changes that took place in the andean cordilleras were related to the depositional and erosional history of the caqueta river in the colombian amazonian lowlands the low terrace sediments consist of sandy and gravelly deposits covered by clays that sometimes contain lenses of peaty material from these organic low terrace sediments seven finite radiocarbon dates were obtained of middle pleniglacial age between 56 000 and 30 000 yr bp the coarse textured basal deposits of the low terrace apparently stem from the early part of the middle pleniglaciai period during which the effective rainfall in the andes was relatively high and the andean glaciers had a considerable extension palynological data from silty sediments with organic remains at one site show an interval when drier and more open types of vegetation on poor soils must have covered a larger area than today but amazonian forest was still the dominating type of vegetation this interval might correspond to one of the middle pleniglacial savanna intervals from eastern amazonia carajas no organic sediments from the upper pleniglacial period were found and hence radiocarbon dates were not obtained in the andes this period had a very cold climate with low effective rainfall and in the east amazonian carajas area it is characterised by the relative extension of open savanna vegetation the river run off and sediment transport must have been much lower than in the middle pleniglacial and the caqueta river cut itself down in its own sediments two late glacial radiocarbon datings obtained at one site ca 12 500 yr bp indicate the existence of a late glacial sedimentation phase separated from the holocene sequence by a minor erosional phase organic layers in the holocene floodplain sediments yielded 28 radiocarbon dates between 10 000 and 355 yr bp holocene sedimentation started with the rapid deposition of sandy clay possibly in a partly permanently inundated caqueta valley during the major part of the holocene silty clays were deposited with a dominant seasonal inundation cycle

neotectonics and tree mortality in a forest ecosystem of the negro basin geomorphic evidence of contemporary seismicity in the intracratonic brazilian amazonia abstract neotectonic activity was increasingly recorded over the amazonian lowlands even during historical times of a few tens of centuries however detailed analyses linking structures and styles of deformation are still few considering the large dimension of the region such events in a relatively recent time are expected to have caused conspicuous impacts on amazonian ecosystems and forest disturbance changes in topography and hydrology by fracturing faulting and folding during either subsidence or uplifting are direct effects on landscape that leave marks on the structure of the current forest such as tree mortality and community succession two rectangular elbow like shaped wetlands from the left margin of the middle negro river valley in northwestern amazonia were attributed to neotectonics remote sensing imagery was applied to test this hypothesis and also provide a tectonic model that can explain deformation dynamics in this area the studied wetlands and adjacent river systems display various morphostructural anomalies compatible with a tectonic control as well as lineaments paralleling main nw and ne trending regional structures the geomorphic analysis led to suggest that the wetlands are depressions formed by nw and ne trending master boundary faults of horizontal displacements intercepted by various subsidiary faults transtensional strike slip regime is recorded by both left and right lateral faults with the wetlands corresponding to subsiding areas owned to conjugate strike slip faults habitat fragmentation and other ecological processes promoted by tectonic deformation would have impacted the overlying forest canopy by changing its structure due to tree mortality the complex compartmentalization imposed by active tectonics would have exposed the ground to contrasting hydrological conditions which controlled the rate of tree mortality within the wetlands we pose that the tectonic disturbance and associated tree mortality documented in the middle negro river evidence contemporary seismicity within the intracratonic brazilian amazonia

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated

floodplain evolution in a confluence zone parana and ivai rivers brazil abstract in this study we investigated floodplain development at the confluence of the parana and ivai rivers brazil we evaluated paleochannels with sedimentary facies and morphometry from cartographic products which enabled us to identify compartments that indicate homologous morphogenesis these results contributed to the distinction in the floodplain of areas reworked by the parana ivai or both river systems additionally investigations that included dating deposits on the terrace that borders the floodplain and an alluvial fan also in contact with the floodplain reinforced the interpretation of the fluvial landscape the identified stages of geomorphological evolution demonstrated the existence of a paleoconfluence of the parana and ivai rivers during the late pleistocene that was located 6 km upstream from the current confluence this paleoconfluence displays a different configuration in relation to the current confluence and its features resemble and contribute to understanding the former braided channel pattern of the parana river the abandonments of the parana river channels identified in this study were initial and crucial process in the development of the floodplain this channel change favored the formation of extensive wetlands and consequently the confluence migration which resulted in the fluvial reworking indicated by the paleochannels of the ivai river another implication from the confluence migration was a base level fall which contributed to maintaining the stability of the ivai river and its embedded meanders in addition investigations of an alluvial fan in the parana river valley provided evidence of massive deposition of sediments from a tributary of the ivai river onto the floodplain which is associated with a regional dry period in the late holocene as well as neotectonic control

two pool to pool spacing periods on large sand bed rivers mega pools on the madeira and mississippi abstract the madeira river thalweg includes two pool to pool spacing periods first standard pool crossing sequences form 6 to 8 m deep pools these pool crossing sequences recur approximately every six channel widths 9 7 km or 6 8 w on average however the madeira study reach between manicore and porto velho in northern brazil is relatively straight making these pools more frequent than meanders second much deeper pools 13 to 30 m deep also form at relatively regular but much longer spacing 50 60 km about 40 channel widths apart the deeper mega pools occur where the river reaches the edge of the holocene alluvium encountering resistant units e g granite mud clasts and conglomerates in the confining pleistocene units these two pool scales also occur on the lower mississippi river downstream of tarbert landing this study identified pool formation processes responsible for these two pool depth and spacing scales on two large sand bed rivers the analyses computed pool statistics and correlated the deepest pools with planform controls two distinct pool formation hypotheses explain the two pool types the standard pools are rhythmic features developed by macro turbulent feedbacks while the mega pools are forced features imposed by the regional geology the former are fundamentally periodic the latter are not however periodogram analysis indicates that mega pools on the madeira form a second relatively regular pool period the regional geology including the confining pleistocene bluffs and potentially orthogonal neotectonic lineaments imposed periodic regularity to these mega pools on the madeira river that is not observed on the mississippi river a comparably sized sand bed river with mega pools

late pleistocene glacial forest elements of brazilian amazonia abstract pollen data recovered from the sedimentary record of western amazonia is still inadequate to fully address climate changes over the last glaciation in this region the present work focuses vegetation dynamics from an area of southwestern amazonia during the past 42 000 cal yr b p based on the integration of previous and new pollen data sediment cores were sampled from two sites covered by tropical rainforest in fluvial terraces of the madeira river a major southern amazonian tributary the results indicated a significant proportion of cold adapted andean tree species represented by alnus 0 20 hedyosmum 1 15 podocarpus 0 5 illex 1 11 and weinmannia 0 1 at least between 43 163 42 018 cal yr b p and 10 394 10 240 cal yr b p during the holocene only pollen representative of herbs and modern amazonian vegetation persisted the new pollen record confirmed previous documented results that vegetation communities presently restricted to andean areas at altitudes higher than 2000 3000 m occupied this region of the amazonian lowlands close to the onset and probably also during the last glacial maximum

mapping exposed and buried drainage systems using remote sensing in the negev desert israel abstract this paper examines the use of optical visible and infrared ir data synthetic aperture radar data sar and ground penetrating radar gpr for detection identification and mapping of exposed and buried channels under sands in the western negev israel and northern sinai egypt field observations and shallow geophysical methods corroborated the observations the halutza agur and shunra sand dunes are the continuation of the northern sinai dunes playa type sediments from the late quaternary are found in upper reaches of dry river channels between the dunes of the northwest negev and represent a deterioration of the drainage system caused by shifting sand dunes a dual polarimetric radar sir c image from srl 1 having two frequencies and two polarizations exhibits meaningful differences in reflectance between the buried and abandoned channels and their surroundings the buried continuation of wadi mobra and the larger nahal nizzana channels under the western shunra sand dunes can be observed in l band radar data these channels are not clearly observed either in the landsat thematic mapper tm visible nor in the near infrared nir images the radar wavelengths and polarizations that improve the contrast between the buried river beds and the surrounding sand mantle are in descending order l hv l hh and c hh however in places where the sand mantle is very thick or where channels cut through bedrock the visible and near infrared data from landsat tm are easier to interpret and tend to be more useful for mapping fluvial patterns

tertiary and quaternary volcanism of the erzurumkars area eastern turkey geochronological data and geodynamic evolution abstract this paper presents new geochemical and geochronological data on the neogene and quaternary volcanic products from the area of erzurum and kars eastern turkey the affinity of most of the volcanic rocks concerned is calc alkaline with the exception of minor quaternary alkaline rocks that outcrop in the kars sector ages range from 8 m y to 1 3 m y the time space distribution of the calc alkaline volcanism in eastern turkey nw iran is characterized by a sudden northward jump that occurred around 6 m y ago from the van erzurum southern belt to the kars northern belt available data indicate that this northward migration of volcanism was due to changes in the subduction geometry of the arabian plate under eurasia

applying dem srtm for reconstructing a late quaternary paleodrainage in amazonia abstract remote sensing is a particularly invaluable tool that has helped the detection of paleomorphologies produced by river dislocation in a variety of landscapes which has contributed in reconstructing the geological evolution of many fluvial systems this technique might provide useful information to discuss the evolution of large fluvial systems in special those located in areas of difficult access where the acquisition of field data is difficult application of remote sensing for paleodrainage characterization in densely vegetated tropical areas is scarce in the literature this work records processing of the digital elevation model dem derived from the shuttle radar topography mission srtm which succeeded in revealing an ancient drainage complex of the madeira river one of the main amazonas tributaries where other remote sensing products failed the detection analysis of this paleodrainage and of its modern counterpart within the geological framework available for this region leads to propose that activity along pre existent faults during the latest quaternary would have promoted the southeastward dislocation of a nearly 200 km long segment of the madeira river during this process an impressive paleodrainage network was left behind which was only able to be detected using the dem srtm application of this technique might be of great help to the detection of paleodrainage morphologies in densely vegetated areas similar to the amazonas lowland the dynamics of channel migration in this and many other large scale tropical river systems might benefit from the investigation based on data derived from dem srtm

mineralogical and geochemical characterization of the saray and pinarhisar coals northwest thrace basin turkey abstract this study investigates the mineralogical and geochemical characteristics of coals from the saray and pinarhisar coalfields in the northwest thrace basin using optical microscopy scanning electron microscopy x ray diffraction and inductively coupled plasma mass spectrometry the saray and pinarhisar coals were deposited in a limnic environment the sulfur content of the coals ranges from 0 3 to 15 3 and high sulfur contents may originate from both seawater and volcanism pyritic and organic sulfur are the dominant sulfur forms 1 2 and 2 7 on average respectively the mineral matter of the coals consists mainly of pyrite barite gypsum muscovite and kaolinite with minor amounts of quartz butlerite tamarugite and rozenite the coals are enriched in trace elements including v 61 ppm on average co 5 85 ppm on average ni 79 ppm on average as 39 2 ppm on average th 3 6 ppm on average and u 6 7 ppm on average based on pearson correlation coefficients ti v cr fe co ni cu se rb au hg pb and th have mainly inorganic affinities r ash elements 0 5 in the pinarhisar coals fe as and au also have inorganic affinities r ash elements 0 5 in the saray coals the element contents and correlation coefficients indicate that the strandja massif the tethyan ophiolite belt and the oldest basement sediments were included in the sediment source region for both coalfields while the strandja massif was the prevailing sediment source region for pinarhisar coalfield

high resolution dem generation from spaceborne and terrestrial remote sensing data for improved volcano hazard assessment a case study at nevado del ruiz colombia abstract volcanoes with rugged terrain remain a challenging target for generating high resolution digital elevation models dems especially in tropical areas with frequent cloud cover using nevado del ruiz volcano as an example we combined dems from the tandem x tdx satellite mission terrestrial radar interferometry tri and structure from motion sfm to generate a new dem with 10 m spatial resolution this is the first study combining satellite radar ground based radar photography and freely available global dems to generate a high resolution dem without data gaps tdx data from ascending and descending orbits were combined to generate the base dem instead of using a raster format to fuse dems generated from different data sets with different resolutions we developed a methodology based on 3 d point clouds 1 re georeference the 5 m tri and 1 m sfm dems to the 10 m tdx dem using the iterative closest point icp algorithm to minimize the horizontal and vertical discrepancy between dems then 2 merge the multiple point clouds to generate a final dem without data gaps using an adaptive algorithm that uses two search distances to smooth the transition at the edges of different data sets we assess the new 10 m dem by comparing simulated inundation zones obtained with two volcano flow models laharz for lahars and volcflow for pyroclastic flows and find significant differences with respect to the 30 m srtm dem our laharz simulation over the new dem shows a longer lahar run out distance for pyroclastic flows the volcflow simulation over the new dem produces highly channelized flows over the steep portions of a river channel and gives a larger extent of thicker deposits compared to those obtained with the 30 m srtm dem quantitative and qualitative geomorphic analysis suggests that up to date dems with high spatial resolution 10 m or even better need to be generated to improve volcano hazard assessment for active volcanoes

the late neogene sahabi rivers of the sahara and their climatic and environmental implications for the chad basin this paper is based on the concept that the drainage system of c 7 5 4 6 ma is still reflected in the geomorphology of northeastern chad and adjacent areas of libya during the messinian and early pliocene a large lake was present in the chad basin that is termed neogene lake chad it fluctuated in size in response to the precessional cycle and at times overflowed to the east ne or north giving rise to the sahabi rivers the eosahabi flowed during the drawdown of the mediterranean late messinian and eroded the erdi and part of the east tibesti valley the post rift miocene deposits of the chad basin some several hundred metres in thickness record a transgression over an irregular and faulted terrain with the deposition of coarse and fine clastic material fluviatile and lacustrine environments are represented at least part of the miocene succession belongs to a phase of late miocene lake development fluctuating climate during the messinian and early pliocene led to repeated changes in the environment of the chad and eosahabi basins with over 100 climatic cycles developed this would favour the development of animal species with high adaptability for example to littoral riparian woodland and savanna habitats

the role of tectonics in the late quaternary evolution of brazil s amazonian landscape tectonic reactivation has long been suggested to have occurred over several areas of the amazonian lowland in the neogene holocene numerous landscape changes documented in this region particularly variations in fluvial dynamics and morphologies have nevertheless been exclusively attributed to climatic fluctuations minimizing the effect of tectonics over the neogene holocene evolution of the amazon basin can result in a distorted interpretation of the sedimentary record and as a consequence equivocal paleoclimatic reconstructions climate has often prevailed as a hypothesis to explain changes in fluvial dynamics possibly due to the still scarce synthesizing publications focusing exclusively on the neotectonic influence over this region the present work provides a review of existing data focusing on quaternary tectonics over a large area of the amazonian lowland the existing information is complemented by original morphostructural data on quaternary terrains from this region which were acquired through remote sensing the goals were to analyze the geographic extent of late quaternary deposits and to determine the impact of tectonics on their development and on the latest evolution of the amazon drainage basin the analysis shows that 1 the amazonian lowland experienced geographically widespread sedimentation in the late pleistocene holocene 2 sedimentation was promoted by the creation of new depositional sites mostly likely resulting from tectonic activity and 3 tectonic reactivation impacted the latest evolution of this entire region with particular influence on drainage basins as revealed by river courses with an abundance of morphostructural lineaments evidencing fault control hence the nw ne nearly n s and to a lesser extent w e morphostructural trends recorded in all areas investigated here are generally associated with strike slip deformation in addition they are conformable with the main orientation of tectonic structures from adjacent crystalline rocks of the precambrian basement they also match tectonic trends documented in neogene and younger sedimentary deposits from this and several other areas of northeastern brazil furthermore some are detected locally in the subsurface by geophysical data furthermore a profusion of morphostructural anomalies is imprinted on the surface of neogene holocene deposits of the amazonian lowland the main ones consisting of 1 highly asymmetric modern drainage basin still undergoing organization with anomalous patterns i e trellis sub dendritic sub parallel and rectangular that often vary from one another frequent river captures and rivers flowing in contrary directions along the time and straight channels that form triangular shapes or triple junctions or with local meandering and subtle enlargements 2 an abundance of channels floodplains lakes and entire valleys with straight and orthogonal margins that locally form rhombic shapes or which may be laterally displaced 3 fluvial rias i e rivers that became enlarged as their mouth were barred bounded by sharp and orthogonal lineaments which result in rectangular shapes 4 termination of megafans into rhombic shaped depressions bounded by straight lineaments or their lateral displacement several kilometers apart and 5 rivers with asymmetric terraces laterally displaced by faults these observations together are consistent with a landscape controlled by neotectonic activity the modern seismogenic record which reveals even high magnitude earthquakes indicates active deformation over the amazonian lowland at the present time the neotectonic history of the amazonian lowland is explained within the context of an overarching mechanism most likely related to intraplate stresses this was probably caused by reactivation of pre existing structures since the neogene that was most likely promoted by activity along oceanic fracture zones and transform faults of the brazilian equatorial margin as well as tectonism in the andean region

the role of tectonics and climate in the late quaternary evolution of a northern amazonian river abstract the amazon basin has most of the largest rivers of the world however works focusing the geological evolution of the trunk river or its tributaries have been only partly approached the branco river constitutes one of the main northern amazonian tributaries a previous work proposed that before flowing southward into the negro amazon rivers the branco river had a southwest to northeast course into the caribbean sea the present work aimed to establish if the proposed change in the course of this river is supported by morphological and sedimentological data other goals were to discuss the factors influencing river development and establish its evolution over time within the chronological framework provided by radiocarbon and optically stimulated luminescence dating the work considered the entire course of the branco river downstream of the precambrian guiana shield where the river presumably did not exist in ancient times the river valley is incised into fluvial sedimentary units displaying ages between 100 and 250 ky old which record active and abandoned channels crevasse splay levees and point bars the sedimentary deposits in the valley include two alluvial plain units as old as 18 7 ky and which intersects a late pleistocene residual megafan these characteristics suggest that a long segment of the branco river was established only a few thousand years ago together with several structural anomalies these data are consistent with a mega capture at the middle reach of this river due to tectonic reactivation in the late pleistocene this integrated approach can be applied to other amazonian tributaries to unravel how and when the amazonian drainage basin became established

geochemical and isotopic changes in the fumarolic and submerged gas discharges during the 2011 2012 unrest at santorini caldera greece a geochemical survey of fumarolic and submerged gases from fluid discharges located in the nea kameni and palea kameni islets santorini island greece was carried out before during and after the unrest related to the anomalously high seismic and ground deformation activity that affected this volcanic system since january 2011 our data show that from may 2011 to february 2012 the nea kameni fumaroles showed a significant increase of h2 concentrations after this period an abrupt decrease in the h2 contents accompanied by decreasing seismic events was recorded a similar temporal pattern was shown by the f cl so4 2 and nh4 concentrations in the fumarolic condensates during the sharp increase of h2 concentrations when values up to 158 mmol mol were measured the 13c co2 values which prior to january 2011 were consistent with a dominant co2 thermometamorphic source have shown a significant decrease suggesting an increase of mantle co2 contribution light hydrocarbons including ch4 which are controlled by chemical reactions kinetically slower than h2 production from h2o dissociation displayed a sharp increase in march 2012 under enhanced reducing conditions caused by the high h2 concentrations of may 2011 february 2012 the general increase in light hydrocarbons continued up to july 2012 notwithstanding the contemporaneous h2 decrease the temporal patterns of co2 concentrations and n2 ar ratios increased similarly to that of h2 possibly due to sealing processes in the fumarolic conduits that diminished the contamination related to the entrance of atmospheric gases in the fumarolic conduits the compositional evolution of the nea kameni fumaroles can be explained by a convective heat pulse from depth associated with the seismic activation of the ne sw oriented kameni tectonic lineament possibly triggered by either injection of new magma below nea kameni island as apparently suggested by the evolution of the seismic and ground deformation activity or increased permeability of the volcanic plumbing system resulting from the tectonic movements affecting the area the results of the present study demonstrate that the geophysical and geochemical signals at santorini are interrelated and may be precursory signals of renewed volcanic activity and encourage the development of interdisciplinary monitoring program to mitigate the volcanic risk in the most tourist visited island of the mediterranean sea

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

high pressure metamorphism in the aegean eastern mediterranean underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone 1 we report 40ar 39ar ages from various tectonic units in the aegean and westernmost turkey on the basis of published geochronologic data and our 40ar 39ar ages we propose that the aegean is made up of several high pressure units which were successively underplated from the late cretaceous until the miocene ages for high pressure metamorphism range from 80 83 ma in parts of the vardar izmir ankara suture zone in the north to 21 24 ma for the basal unit in the cyclades and the external high pressure belt on crete in the south published seismic data suggest that high pressure metamorphism is currently occurring underneath crete younging of high pressure metamorphism in a southerly direction mimics the southward retreat of the hellenic subduction zone we propose that distinct stages of high pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat by far most of the exhumation of the high pressure units occurred early during the orogenic history in a forearc position

a tectonically triggered late holocene seismite in the southern amazonian lowlands brazil abstract definitive criteria for identifying the triggers of soft sediment deformation structures ssdss from sedimentary deposits are still under construction in this work we aimed to contribute to advancing this issue describing the sedimentological characteristics of an interval of ssdss formed in a region of the amazonian lowlands having numerous morphostructural evidences of neotectonic reactivation the deformed interval is 1 5 m thick and consists of load and flame structures interbedded with massive beds sandwiched between well stratified deposits of a fluvial sandy channel succession with a radiocarbon age of 1301 1382 cal yr bp the ssdss are intercepted by numerous small scale normal graded faults the most interesting is that these faults display segmented nw se trending planes that propagate upward after horizontal displacements of a few millimeters processes intrinsic to channel dynamics could not justify this fault morphology which is related to recurrent short lived seismic perturbations with intervening sedimentation following a main tremor a relation to fault reactivation is proposed with basis on the fault trend compatible with the regional structural pattern and the numerous morphostructural anomalies verified in the study area including trellis and sub trellis drainage rectangular and to a less extent annular channels anomalously enlarged channels orthogonal channels and valleys channel captures sudden changes in channel morphology moderate to high basin asymmetry factor af between 10 and 27 moderate to high transverse topography symmetry factor t 0 3 0 5 and anomalous longitudinal river profiles with concavity values 11 to 30 indicative of rivers in process of adjustments the morphology of the fault graded beds described herein might constitute a feature of relevance for identifying seismites in other fluvial deposits

the holocene alluvial plain of the middle amazon river brazil abstract the fluvial belt of the amazon river is a complex of quaternary sedimentary units of different ages and formation conditions present position of the channel and the morphology and size of the alluvial plain are related to neo tectonic lineaments in the study area the main channel of the solimoes is nearly straight the river may be considered anastomosed albeit with few islands and anabranches the main holocene units are the impeded floodplain and the channel dominated floodplain the channel dominated floodplain is a complex mosaic of fluvial forms including younger channels active sandbars islands levees scroll dominated plains and abandoned belts the impeded floodplain is a widespread unit characterised by a very flat surface and round or irregularly shaped lakes the impeded drainage flood plain is only partially affected by the present floods and even those parts affected by floods receive little or no sediment from the main channel more important sediment contribution is by alluvial plain channels from the solimoes branches that generate deltas in the impeded floodplain lakes the impeded floodplain is interpreted to be an earlier stage in the evolution of the holocene alluvial belt the formation was marked by widespread vertical accretion and a channel morphogenetically less active than at present the later stage is associated with an active main channel and the paranas and generation of a scroll dominated plain this very large river system had a complex and delayed response to variations in the hydrological conditions induced by changes in the regional climate during the late holocene

a late pleistocene holocene wetland megafan in the brazilian amazonia abstract despite the growing interest in megafans definitions provided for this type of environmental setting have not yet been widely agreed upon a record of sedimentary facies distribution in both space and time including a larger number of analogs is particularly needed for improving megafan facies models this work focuses on a large fan like feature from an amazonian wetland in northern brazil morphological data based on remote sensing as well as sedimentary facies and radiocarbon analyses were integrated to propose that this feature is related to a megafan system active during the late pleistocene to holocene the megafan displays a divergent drainage network gently dipping slope and concave up and convex up longitudinal and transverse profiles respectively near surface deposits correspond to fining and coarsening upward sands related to active channels and overbank sand sheets terminal fan lobes sediments are interbedded with abandoned channel floodplain and lake pond muds morphostructural analyses and drainage anomalies revealed a geological setting affected by reactivation of pre existing faults contemporaneous with sediment accumulation establishment of a megafan system in this wetland most likely occurred within a slightly tectonically subsiding basin under favorable climatic conditions during wet seasons high water discharge would have favored sediment transport from highlands into this depositional site high summer temperatures and drought under a monsoonal regime kept the water levels low the described megafan could serve as an analog for contemporary tropical wetland megafans formed under a monsoonal climate regime

a new method for supporting interpretation of paleochannels in a large scale detrended digital elevation model interpretation abstract in ancient china the course of rivers changed frequently under the influence of the natural environment the study of changes in paleochannels provides the basis for river regulation and water conservancy and also supplies an important scientific foundation for the evolution of the geographical environment however it is extremely difficult to determine the location of paleochannels due to the limitations of traditional research methods and modern remote sensing interpretation this paper introduces a new method detrended digital elevation model interpretation for supporting interpretation of ancient rivers at large scales a detrended dem was obtained by removing the overall trend from the original dem by subtracting a detrending surface derived from the original image using a guiding filter the paleochannels of the yellow river in the north china plain were interpreted by gis analysis with the help of historical materials the detrended dem was found to be less affected by the surface environment and had higher identification accuracy compared with an optical image and the colored dem moreover the detrended dem could be used to interpret ancient rivers at large scales finally the flow path of ancient rivers in the eastern han dynasty or near the jindi river was hypothesized using the interpretation results the resulting paleochannel data can be used to revise historical river maps and provide reference for researching and managing the yellow river

source mechanisms of moderate size earthquakes and stress orientation in mid plate south america summary fault plane solutions of six mid plate earthquakes with magnitudes ranging from 4 8 to 5 5 mb were determined using p wave first motion data and the relative amplitudes of short period teleseismic depth phases pp and sp these results together with previous studies show a predominance of reverse and strike slip faulting indicating horizontal compressional stresses in mid plate south america the orientation of the p axes however is not uniform in western and southwestern brazil the p axes are oriented approximately e w probably due to the nazca south america plate convergence in eastern brazil the direction of the p axes show more scatter but an average e w direction is consistent with the available data on the contrary in northern brazil the p axes of two events in the amazon basin trend approximately n s a direction perpendicular to the direction of absolute plate motion as well as to the relative plate motions nazca south america and south america africa

the role of late pleistocene holocene tectono sedimentary history on the origin of patches of savanna vegetation in the middle madeira river southwest of the amazonian lowlands abstract savanna patches are features of the amazonian landscape that have been long under intense debate but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix in particular their geological substrates were poorly documented the aim of this work is to reconstruct the tectono sedimentary history of four savanna patches in the middle madeira river southwest amazonia and discuss its potential control over the development of the savanna communities the approach consisted in the integration of geomorphological sedimentological chronological and floristic data the results revealed that the savanna substrates are sandy deposits aged between 118 9 and 35 6 ky overlain by late pleistocene to holocene muddier successions

global warming and fluvial geomorphology future global warming has a number of implications for fluvial geomorphology because of changes in such phenomena as rates of evapotranspiration precipitation characteristics plant distributions plant stomatal closure sea levels glacier and permafrost melting and human responses potential changes in rivers are outlined in this review in the context of changes in the intensity of rainfall the activity of tropical cyclones runoff response including that of europe dry lands and high latitude environments and geomorphological reactions including rates of soil erosion in general however much work remains to be done to establish the full range of geomorphological responses that may take place in fluvial systems

middle to late holocene paleochannels and migration of the palar river tamil nadu implications of neotectonic activity abstract geomorphic tectonic and sedimentary investigations have been carried out to understand the landscape evolution of the palar river basin southern peninsular india for this purpose satellite data interpretations coupled with field investigations fluvial architecture and optically stimulated luminescence osl dating methods were adopted to infer climatic variations and neotectonic deformation that took place during the mid to late holocene period several paleochannels have been identified in the northern part of the present day palar river the distribution pattern of the palar paleochannels and its present course indicate its migration towards the south leaving behind the old palar river streams as paleochannels significant changes in the morphological characteristics channel width and river pattern in the successive paleochannels reveal evidences of channel movement by avulsion largely controlled by reactivation of pre existing lineaments and intensified ne monsoon based on osl ages two major phases of migration have been identified that occurred between 4 83 ka to 1 88 ka first phase occurred between 3 59 ka to 3 26 ka due to intensified monsoon accompanied with small scale neotectonic activity the second phase took place between 2 42 ka to 1 88 ka which occurred probably due to the rapid upstream avulsion this rapid avulsion is due to the close proximity of mpa and the reactivation of the pre existing lineaments moreover the present palar river basin exhibits evidences of neotectonic activity such as soft sediment deformation structures anomalous drainage deflections and reactivation of lineaments and faults further indicating that the palar river is still draining a tectonically active region thus neotctonics and fluctuations in the intensity of monsoon are largely responsible for sculpting the present landscape

the late quaternary evolution of the negro river amazon brazil implications for island and floodplain formation in large anabranching tropical systems abstract the rio negro has responded significantly in the late pleistocene and holocene to lagged environmental changes largely associated with activity during the last glacial in the amazon basin on the basis of geological structure the rio negro can be divided into six distinct reaches that each reflects very marked differential processes and geomorphological styles no deposits of the upper pleniglacial were recognized in the field the oldest recognizable late pleistocene alluvial unit is the upper terrace of middle pleniglacial age ca 65 25 ka reach i tentatively correlated with the oldest terrace identified on the left bank of reach iii at that time the river was mainly an aggradational bed load system carrying abundant quartz sand a product of more seasonal conditions in the upper catchment the late glacial 14 10 ka is represented by a lower finer grained terrace along the upper basin reach i which was recognized in the tiquie curicuriari and vaupes rivers at that time the river carried abundant suspended load as a response to climatic changes associated with deglaciation since about 14 ka the river has behaved as a progradational system infilling in downstream series a sequence of structurally controlled sedimentary basins or compartments creating alluvial floodplains and associated anabranching channel systems reach ii was the first to be filled then reach iii both accumulating mainly sand fine deposits increase downstream in reach iii and become predominant in some anabranch islands of the distal reach the lowermost reaches of the negro v and vi have been greatly affected by a rising base level and associated backwater effect from aggradation of the amazon during late glacial and recent times reach v has acted almost entirely as a fine sediment trap the remarkable anavilhanas archipelago is the product of holocene deposition in the upper part of this sedimentary basin however suspended sediment load declined about 1 5 ka prior to the lower part of this basin becoming infilled the progradational behavior of the rio negro filling tectonic basins as successive sediment traps with sand in the upper basins and fines in the downstream ones illustrates how a large river system responses to profound changes in late quaternary base level and sediment supply the most stable equilibrium conditions have been achieved in the holocene in reaches iib and iiia where an anabranching channel and erosional relictual island system relatively efficiently convey water and sediment downstream reaches iiib and v never achieved equilibrium conditions during the holocene characterised as they are today with incomplete floodplains and open water

variation in noble gas isotopic composition of gas samples from the aegean arc greece abstract in contrast to most other arcs with oceanic plate subduction the aegean arc is characterized by continent continent subduction noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc 2 islands in the back arc region and 7 sites in the surrounding areas the 3he 4he ratios of the samples ranged from 0 027ra to 6 2ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 demonstrating that even the maximum 3he 4he ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems which are equal to the morb value of 8 1 ra regional variations in the 3he 4he ratio were observed both along and across the arc the maximum 3he 4he ratio was obtained from nisyros volcano located in the eastern end of the arc and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano across the volcanic arc the 3he 4he ratio decreased with an increasing distance from the arc front reaching a low ratio of 0 063ra in macedonia which suggested a major contribution of radiogenic helium derived from the continental crust at nisyros a temporal increase in 3he 4he ratio due to ascending subsurface magma was observed after the seismic crisis of 1995 1998 and mantle neon was possibly detected the maximum 3he 4he ratio 6 2ra in the aegean region which is significantly lower than the morb value is not probably due to crustal assimilation at shallow depth or addition of slab derived helium to morb like mantle wedge but inherent characteristics of the subcontinental lithospheric mantle sclm beneath the aegean arc

modern sedimentation in the lower negro river amazonas state brazil abstract the negro river which flows through the north central amazon basin is one of the largest tributaries of the amazon the name negro comes from the colour of its water which reflects the large quantity of dissolved humic acids and iron oxides that also gives the water its characteristic acid ph the river is estimated to have the fifth largest water discharge in the world about 30 000 m3 s the negro river is characterized by a high dissolved load but a low energy system neotectonics and water quality are the principal factors that control the modern sedimentation in the lower negro river the lower negro river is controlled largely by a nw se tectonic lineament that is a segment of a major tectonic transcurrent dextral megasystem of the amazon basin neotectonism in this area is responsible for the depth of the river and for the occurrence of steep falesias cliffs along some parts of its borders it also seems that neotectonics have influenced the origin of the anavilhanas islands which are a series of anastomosed elongated silty clayey channel bars with internal round or long narrow lakes the igapo which is the forested area flooded during part of the year appears to have a neotectonic origin as well igapos are located on intermediate blocks between the high blocks of the terra firme and the low blocks of the channel the absence of clastic sediments carried in suspension is related to the rare appearance of floodplains which are limited to very thin layers of fine sediments located on the abrasion shelfs carved in clastic deposits of the alter do chao formation sand bars occur in places along the base of the cliffs and along the edges of the channel system these sand bars are composed of quartz sand derived from the reworking of the sand of the alter do chao formation

imaging underwater neotectonic structures in the amazonian lowland previous documentation has proposed tectonic activity from the neogene to holocene as one important control on drainage development in the amazonian lowland however recording tectonic structures in this region has been challenging due to environmental difficulties including the low topography and dense vegetation cover that do not favor natural exposures for this reason the role of tectonics in determining river dynamics morphology and sediment deposition in amazonia has been suggested with caution despite limitations morphostructural lineaments have provided useful information to support fault reactivation in several areas of the amazonian lowland however further documentation is required to map the faults and describe their geometry this approach is essential to better understand the geotectonic model of this region in this work analyses of high resolution optical imagery of three amazonian shallow water lakes provided exceptional views of an abundance of linear features on the beds of the

the aegean sea we summarize briefly the main features of a kinematic model of evolution of the aegean area since 13 ma the formation of the aegean sea by extensional tectonics is related to the subduction of the mediterranean floor below the hellenic arc we then make a quantitative estimate of vertical movements in the aegean area on the basis of geological data and demonstrate that the outer arc was built since the beginning of this episode of subduction by vertical uplift the easiest way to explain the uplift is by underplating finally we discuss briefly the dynamics of the subduction marginal sea formation processes in this continental collision framework

geochemistry and alteration facies associated with epithermal precious metal mineralization in an active geothermal system northern lesbos greece hydrothermal quartz veins associated with gold and silver mineralization and variable amounts of base metal sulfides have been discovered within an active geothermal system in the megala therma area of northern lesbos this geothermal system is proba bly a late evolutionary stage in the formation of this mineralization the veins are hosted in upper miocene volcanic rocks of andesitic composition and consist of quartz adularia chlorite sericite illite kaolinite baryte small amounts ofjarosite and alunite and native gold pyrite galena sphalerite chalcopyrite bornite chalcocite covellite and goethite the principal types of alteration which occur in the studied area are silicification propylitization argillic alter ation and potassic phyllic alteration

new geological framework for western amazonia brazil and implications for biogeography and evolution abstract although many of the current hypotheses to explain the origin and distribution of the amazon biodiversity has been based directly or indirectly on geological data the reconstruction of the geological history of the amazon region is still inadequate to analyze its relationship with the biodiversity this work has the main goal to characterize the sedimentary successions formed in the brazilian amazon in the neogene quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap radar image interpretation sedimentological studies and radiocarbon dating allowed the mapping of plio pleistocene to holocene units along the solimoes amazonas river brazil this integrated work led to the characterization of five sedimentary successions overlying miocene deposits of the solimoes pebas formation which include the following ica formation plio pleistocene deposits q1 37 400 43 700 14c yr b p deposits q2 27 200 14c yr b p deposits q3 6730 2480 14c yr b p and deposits q4 280 130 14c yr b p these deposits occur mostly to the west of manaus forming nw se elongated belts that are progressively younger from sw to ne indicating a subsiding basin with a depocenter that migrated to the ne the reconstruction of the depositional history is consistent with significant changes in the landscapes hence the closure of a large lake system at the end of the miocene gave rise to the development of a plio pleistocene fluvial system this was yet very distinct from the modern drainage with shallow energetic highly migrating braided to anastomosed channels having an overall northeast outlet this fluvial system formed probably under climatic conditions relatively drier than today s during the early pleistocene there was pronounced erosion followed by a renewed depositional phase ca 40 000 14c yr b p with the development of prograding lobes and or crevasse splays associated with a lake system i e fan delta and or fluvial flood plain areas after a period of erosion a fluvial system with eastward draining channels started to develop at around 27 000 14c yr b p the fluvial channels were overflooded in mid holocene time this flooding is attributed to an increased period of humidity with a peak between 5000 and 2500 14c yr b p the data presented herein support that rather than being a monotonous area the amazonia was a place with frequent changes in landscape throughout the neogene quaternary probably as a result of climatic and tectonic factors we hypothesize that these changes in the physical environment stressed the biota resulting in speciation and thus had a great impact on modern biodiversity

provenance of sands from the confluence of the amazon and madeira rivers based on detrital heavy minerals and luminescence of quartz and feldspar abstract source to sink systems are poorly known in tropical rivers for the amazonian rivers the majority of the provenance studies remain focused on the suspended load implying a poor understanding of the processes governing production and distribution of sands in this study we perform heavy mineral and optically stimulated luminescence osl analysis to cover the entire spectrum heavy and light minerals fraction of 29 sand samples of the lower madeira river region amazon and madeira rivers of which the main goal was to find provenance indicators specific to these rivers despite the tropical humid climate the sands of the amazon and lower madeira rivers are rich in unstable heavy minerals as augite hypersthene green hornblende and andalusite the madeira river is highlighted by its higher content of andalusite with source attributed to the amazon craton medium to high grade metamorphic rocks while the amazon river upstream of the madeira river mouth has a signature of augite and hypersthene that suggests an andean provenance volcanic rocks sands from the madeira river can be tracked in the amazon river by the increasing concentration in andalusite osl analysis of the light minerals fraction was used as an index of feldspar concentration and sedimentary history of quartz grains lower feldspar concentration and quartz grains with longer sedimentary history higher osl sensitivity also point to a major contribution of cratonic sources for the sands in the madeira river while the sands from the lower madeira would be mainly supplied by cratonic rocks previous work recognised that suspended sediments silt and clay are derived from andean rocks therefore we interpret a decoupling between the sources of sand and mud silt and clay under transport in the madeira river andean sands rich in augite and hypersthene would be trapped in the foreland zones of the beni and mamore tributaries in the amazon river sands the low osl sensitivity of the quartz higher content of feldspar and unstable heavy mineral assemblage dominated by augite and hypersthene suggest both a fast transport from andean sources with fine sediment bypass over foreland areas

miocene fish faunas from the northwestern amazonia basin colombia peru brazil with evidence of marine incursions new evidence indicates marine influences during the miocene in the northwestern amazonia basin this is the first major survey of the ichthyofauna from this area in the miocene fossil fish remains from taxa such as the dasyatoidea myliobatoidea characiformes siluriformes and sciaenidae are found conspicuous finds were two pharyngeal teeth of stephanodus minimus a species that so far had only ever been found in late cretaceous sediments the fish remains of freshwater brackish and marine taxa are deposited together throughout the area this is thought to be related to marine influences during the miocene these finds agree with earlier studies that suggest episodic marine influences which most likely lasted up to the late miocene and disagree with studies that suggest a connection between the atlantic and the caribbean sea over the south american continent the ichthyofaunas also indicate a warm climate as well as shallow and possibly torrential waters c 1998 elsevier science b v all rights reserved

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation

tectonic stages along a traverse cross cutting the rhodopian zone greece in a cross section along the rhodopian zone from the greece bulgarian border through the postalpine basins in the xanthi area to thasos island detailed structural mapping and collection of field data enable us to determine a sequence of tectonic stages that affected this area this allows us to propose a model of continental collision during the early eocene ne sw directed movements produced a southwest facing pile of crystalline nappes with internal deformation comprising nw and ne trending isoclinal folds and a ne sw trending stretching lineation after a short time interval nappe movements started again under brittle deformation conditions and produced composite thrust sheets wnw and nne trending chevron folds and thick cataclasite late erogenic uplift and extension caused the formation of nw and ne trending normal faults these faults bounded the oligocene flysch and molasse basins and provided pathways for voluminous magmatic suites this tectonic process was interrupted at the oligocene miocene boundary by a late orogenic compression reflected in nw open folds and dissolution cleavages subsequently differential uplift and subsidence associated with nw and ne trending normal faults has continued up to the present time from the early pliocene new fragmentation and thinning of the crust reflected in wnw listric faults and nne transfer faults has affected the southern parts of the rhodopian zone nappe forming movements are the result of a progressive collisional process involving a kimmerian microcontinent lying between the eurasia and apulia continents in the final stages of this collision uderplating processes led to regional uplift and extension additional extensional movements were related to the formation of the aegean back arc basin caused by the late cenozoic hellenic subduction zone