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

pre neogene controls on present day fault activity in the west netherlands basin and roer valley rift system southern netherlands role of variations in fault orientation in a uniform low stress regime the west netherlands basin wnb and the neighbouring roer valley rift system rvrs form the most prominent tectonic features of the onshore netherlands the two basins have a common tectonic origin and similar mesozoic evolution their neogene quaternary evolution however is markedly different while the wnb is tectonically seismically inactive and is characterised by uniform neogene quaternary subsidence in the rvrs fault controlled intra plate deformation has taken place since late oligocene times with pronounced seismic activity considering the present day ne sw regional extension as well as the similar basin orientation and mesozoic evolutions one would not expect strikingly different neotectonic activity in the two basins detailed analysis of mesozoic tertiary and quaternary fault patterns revealed that 1 the palaeozoic mesozoic tectonic fabric has great influence on the cenozoic deformation style of the basin system 2 present day faulting in the rvrs is related to the reactivation of pre existing faults and 3 the mesozoic fault pattern is slightly different in the two basins using a novel technique three dimensional 3 d slip tendency analysis we aim to determine whether these differences in fault orientation are substantial enough to produce significantly different resolved stresses along the faults this modelling not only tests a common geological phenomena but indirectly also delivers important constraints regarding the origin of faulting in the study area during the analysis 3 d geometric models of 84 mapped faults were investigated the results of this recently developed modelling technique reveal that the faults in both basins should behave similarly under the condition of a laterally homogeneous regional stress field which is in disagreement with the present day tectonic activity of the region on the other hand the modelling also reveals that the predicted tendency of slip is very sensitive to the ratio of the minimum horizontal and the vertical stress s as an explanation for the pronounced fault activity in the rvrs and the tectonic quietness of the wnb it is proposed that either the regional extension in the wnb is weaker in term of higher s ratio than that in the rvrs or the slip thresholds in the two basins are different the study emphasised that differentiation in the tectonic evolution has already started in the tertiary therefore it is reasonable to assume that the different tectonic stress field and or slip threshold between the two areas is directly related to the origin of the cenozoic rifting in the rvrs several hypotheses are discussed to account for these two possibilities taking into account the lithospheric structure and the cenozoic tectonic evolution of the two basins as well as surrounding areas 2004 elsevier ltd all rights reserved

near field sea level variability in northwest europe and ice sheet stability during the last interglacial global sea level during the last interglacial lig marine isotope sub stage 5e peaked between c 5 5 and 9 m above present implying significant melt from greenland and antarctica relative sea level rsl observations from several far and intermediate field sites suggest abrupt fluctuations or jumps in rsl during the lig highstand that require one or more episodes of ice sheet collapse and regrowth such events should be manifest as unique sea level fingerprints recorded in far intermediate and near field sites depending on the source s of ice mass change involved to date though no coherent evidence of such fluctuations has been reported from near field rsl studies in northwest europe this is an important problem because rsl fluctuations during the lig are portrayed as warning signs for how polar ice sheets may behave in a future warmer than present world here we review the evidence for rsl change during the lig using stratigraphic data from the best resolved highstand records that exist in the near field of northwest europe from a range of settings that include lagoonal shallow marine tidal flat salt marsh and brackish water fluviatile environments consideration of previously published stratigraphic records from two sites in the eemian coastal marine embayment that existed in the central netherlands yields no clear indications for abrupt rsl change during the attainment of the near field highstand nor do we find any such indications common to other records from countries bordering the north sea the baltic sea and the white sea two modelling experiments that explore the global signal of hypothetical sea level oscillations caused by partial collapse and regrowth of either the greenland or antarctic lig ice sheet show that the north sea region is relatively insensitive to mass changes sourced from greenland but should clearly register events with an antarctic origin especially those that occur late in the lig the lack of evidence for abrupt sea level fluctuations at this time in northwest europe concurs with a lack of clear near field evidence for ice sheet collapse

elevation modelling and palaeo environmental interpretation in the siwa area egypt application of sar interferometry and radargrammetry to cosmo skymed imagery abstract digital elevation models produced from cosmo skymed imagery were used to delineate palaeo drainage in a wide area surrounding the siwa and al jaghbub oases of the western sahara desert egypt and libya this new generation of synthetic aperture radar imagery is suitable for this purpose because of its high spatial resolution and capacity to penetrate dry surface sediments different techniques such as radar interferometry and radargrammetry were used to produce digital elevation models these were assessed for accuracy and then combined to produce a single elevation model of the area the resulting elevation model was used to support the geological study and palaeo environmental interpretation of the area it revealed buried features of the landscape including inactive palaeo drainage systems drainage features were extracted from the elevation model using geographical information systems results were combined and assessed with respect to geological field data as well as data from the literature previous studies in the area suggest that a wide river probably the old nile river flowed into the libyan palaeo sirte before the late messinian drawdown of the mediterranean sea during the late messinian lowering of the sea the fluvial system changed shape and carved deep canyons throughout north eastern africa the reported findings on the key siwa area were used to precisely delineate the physiography of the modern drainage network and to confirm findings from our previous geological research in the area

neotectonic activity in and around the southwestern rhenish shield west germany indications of a levelling comparison abstract precise levelling data are re examined in the southwestern rhenish shield and its foreland by comparing them analytically along levelling profiles instead of generalizing regional vertical movement trends this method emphasizes the activity of individual structural elements which can be located with a high accuracy it is shown that present day vertical motions concentrate on fractures which cut the massif into a number of tectonic blocks these undergo more or less independent movements significant measured displacements range from 1 to 3 5 cm over an average 20 year period and correspond mostly to aseismic slip high displacements are found near pre existing faults sometimes also zones of joint concentration which are favourably oriented with respect to the current regional stress field in the mosel area sw ne trending faults are predominantly reactivated as reverse faults the motion inferred for the hunsruck border fault is also consistent with the compressive regime presently observed in that area with 1 oriented to the northwest the direction of vertical motions along the western border fault of the upper rhine graben changes from south to north in relation to the different azimuths of the central and northern segments of the graben inducing a s n oriented transition from compressional to extensional shear within the graben itself some n160 e trending normal faults are identified one of them having probably ruptured in a swarm of microearthquaks not long before the second survey was performed the western saar nahe trough is characterized by n s oriented fractures which cannot be related to mapped faults but show a close connection with photolineaments

paleocave carbonate reservoirs origins burial depth modifications spatial complexity and reservoir implications paleocave systems form an important class of carbonate reservoirs that are products of near surface karst processes and later burial compaction and diagenesis features and origins of fractures breccias and sediment fills associated with paleocave reservoirs have been studied in modern and ancient cave systems information about such cave systems is used in this paper to reconstruct the general evolution of paleocave reservoirs and their associated scale pore networks and spatial complexities spatial complexities in paleocave reservoirs result from near surface and burial processes near surface processes include dissolutional excavation clastic sedimentation chemical precipitation and localized fracturing brecciation and collapse of cave walls and ceilings burial processes begin as cave systems subside into the subsurface remaining cave passages commonly collapse and early formed breccia clasts are rebrecciated differential compaction of strata around and over collapsed passages produces fractures crackle breccias and mosaic breccias near surface and burial processes combine to produce typically complex reservoirs with several scales of heterogeneity hydrocarbon reservoirs of paleocave origin are commonly the product of coalesced collapsed paleocave systems the coalescing of passages in a cave system into larger connected porosity zones results from a combination of multiple cave forming episodes at composite unconformities and from the collapse of cave systems during burial where surrounding host strata are brecciated and fractured this combination of processes creates spatially complex reservoirs that can be hundreds to several thousands of meters across commonly forming large exploration targets final size pore network types and spatial complexities of coalesced collapsed paleocave systems are products of their evolution from near surface development through burial into the deeper subsurface the coalesced collapsed paleocave reservoir hypothesis explains the scale of reservoirs observed and the spatial complexities involved

intraplate deformation in western europe deduced from an analysis of the international terrestrial reference frame 1997 itrf97 velocity field although tectonic deformation in western europe is essentially concentrated in the appenines and alpine alps pyrenees mountain ranges several large historical and instrumentally recorded earthquakes m 6 are known in the supposedly stable part of europe because of its accuracy and internal consistency at a global scale the international terrestrial reference frame 1997 itrf97 velocity field allows testing of intraplate rigidity in western europe at a millimeter per year level using the full statistical information available on the itrf97 velocities we identify a subset of sites located in central europe that satisfies a rigid cap rotation with residual velocities 1 mm yr and therefore provide a stable europe reference frame serf in this reference frame we find residual velocities at european itrf sites that are consistent with known active tectonic features we identify a northward motion at sites located in italy with internal deformation of the adriatic block rather than rigid plate motion and a westward motion of the westernmost part of europe of the order of 1 2 mm yr relative to central europe the relative motion of the adriatic block and western europe agrees with the current extension known in the tyrrhenian sea and the apennines in central europe we find active deformation 1 mm yr in the eastern alps and western carpathians in the alpine range our results indicate e w extension across the western alps and n s compression across the central and eastern alps in agreement with the strain regime deduced from seismotectonic observations in belgium and the netherlands we find residual velocities of 1 1 5 mm yr to the northwest at all the sites most likely accommodated along the upper and lower rhine graben structures an important outcome of this study is the identification of internal deformation of the order of 1 2 mm yr in an area usually interpreted as stable europe this result should be further checked as new denser and more accurate space geodetic data sets with longer observation time spans become available for europe

evidence for active tilting of the nw german basin from correlations between fluvial landscape and geological subground the catchment basin of the river hunte lower saxony nw german basin was studied on a mesoscale length of 90 km to investigate the influence of the geological subground on modern morphology a geo information system gis was used to calculate linear correlation coefficients between the depth of geological strata base zechstein to base quaternary and the height of the modern landscape holocene alluvial plain lower weichselian terrace catchment basin and watershed high linear correlation coefficients between the base of tertiary and the height of the modern topography catchment basin r2 0 87 lower weichselian terrace r2 0 95 and holocene alluvial plain r2 0 95 indicate control of the modern topography by the depth of the geological subsurface via tilting of the entire basin most likely northward tilting of the nw german basin forces the river hunte to flow in a northerly direction by relative uplift of the hinterland wiehengebirge rhenish massif and subsidence of the north sea area

fluvial evolution of the rhine during the last interglacial glacial cycle in the southern north sea basin a review and look forward this paper presents the current state of knowledge on the evolution and depositional history of the river rhine in the southern part of the north sea basin during the upper middle and late pleistocene and its response to climate change sea level oscillation and glacio isostasy the study focuses on the development of the eemian interglacial lower delta in the central netherlands and its relation to records of climate and sea level rise and uses the saalian and weichselian pre and postdating periods to place its development in context the rhine fluvial system fills the gradually subsiding north sea basin but its development has strongly been affected by the saalian glaciation and its remaining topography ice pushed ridges originating off the limit of maximum glaciation basically divided the central netherlands into two sedimentary depocentres a central depocentre within the former ice limit and a southern depocentre south of it the sedimentary record of the central depocentre including an incised valley fill shows a 20 40m thick stacked sequence consisting of three units the incised valley fill consists of a late saalian to early eemian age lower fluvial unit and a weichselian age upper fluvial unit both composed of coarse grained channel deposits sandwiched in between is a 5 15m thick record composed of fine grained fluvial and estuarine tidal floodbasin and shallow marine deposits it is of eemian interglacial and early weichselian age and comprises transgressive and highstand deposits that show the drowning of a fluvial system inland parts transformed from fluvial to deltaic and estuarine environments and the most downstream parts transformed to a shallow marine embayment preservation of these units occurred despite considerable sea level fall and climate controlled erosion taking place in the last glacial preservation potential was increased by the fact that the rhine system avulsed away to the southern depocentre halfway the weichselian pleniglacial consequently the infill of the southern depocentre is of an entire different nature and last interglacial transgressive or highstand units are hardly preserved because of glaciation and resulting depocentre configuration the netherlands in nw europe thus offers a very good opportunity to study the transgressive interglacial lower deltaic records and falling stage preservation thereof both key elements for understanding sedimentary development over full 100 ky glacial interglacial cycles of climate and base level change 2014 elsevier ltd and inqua

dense shelf water cascading and messinian canyons a new scenario for the mediterranean salinity crisis the salt giant beneath the deep mediterranean seafloor is the impressive record of the messinian salinity crisis a dramatic event that occurred about 6 ma ago following the reduction of the connections with the atlantic ocean according to the shallow water deep basin model developed for these deposits hsu and others 1973a 1973b 1978a 1978b the messinian evaporites formed in a deep but desiccated mediterranean while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown deeply incised messinian canyons in the continental slopes surrounding the mediterranean are the main argument supporting this scenario using a state of the art model and idealized but realistic numerical simulations here we demonstrate that the activation of downslope flows of hypersaline dense waters in a process similar to present day dense shelf water cascading but much more energetic may account for both slope erosion and progressive salinity rise leading to the formation of deep seated supersaturated brines our findings support a deep water deep basin model schmalz 1969 1991 de benedetti 1976 1982 dietz and woodhouse 1988 thus implying that evaporite deposition may have occurred in a non desiccated basin with strongly reduced ocean connections

late pleistocene evolution of the rhine meuse system in the southern north sea basin imprints of climate change sea level oscillation and glacio isostacy high resolution continuous core material geophysical measurements and hundreds of archived core descriptions enabled to identify 13 late pleistocene rhine meuse sedimentary units in the infill of the southern part of the north sea basin the netherlands northwestern europe this sediment record and a large set of optical stimulated luminescence dates 14c dates and biostratigraphical data allowed to establish detailed relationships between climate change sea level oscillation glaciation history and the sedimentary development of the rhine fluvial system during the last glacial cycle marine isotope stages 5e 2 eemian weichselian a well preserved eemian sediment record was encountered as the infill of a late saalian mis6 subglacial basin part of this record reflects groundwater rise controlled fine grained sedimentation as a result of postglacial early eemian sea level rise it shows strong analogy to developments known from the holocene rhine meuse delta outside of the glacial depressions near coastal deposits are only fragmentarily preserved the early glacial rhine sediment record is dominated by organic debris and peat layers marking landscape stability and low fluvial activity part of this record may have been formed under near coastal conditions significant amounts of reworked marine biomarkers in the lag deposits of early pleniglacial mis4 fluvial systems indicate that this period is characterized by extensive reworking of older mis5 near coastal sediments despite the marked early pleniglacial climatic cooling input of new sediment from the drainage basin was relatively low a feature that is related to the presence of regolith protective relic soil complexes in the basin during the early middle pleniglacial a major rhine avulsion indicates the system was in an aggrading mode and that sediment supply into the lower reaches of the rhine had strongly increased this increase in sediment supply coincided with the timing of major climate cooling that occurred from 50 to 45 ka onwards the increase in sediment supply is related to final breakup of the soil complexes in the drainage basin after 24 ka a strong input of coarse grained gravelly sediments was observed which indicates a strong increase in physical weathering processes and periglacial controlled supply of bedload sediment in the catchment a time delay between climate change 30 ka and channel belt aggradation 24 ka is explained as a result of transport path length between source and sink and or effects of higher continental runoff rates after 22 ka the late middle pleniglacial late pleniglacial and lateglacial rhine meuse record testifies for strong influence of glacio isostatic controlled differential upwarping of the study area glacio isostatic controlled forebulge upwarping and lateral valley tilting is shown to have deflected rhine meuse channel belts after 35 ka glacio isostatic upwarping is seen as the main cause for strong incision during the first phase of the late pleniglacial 30 24 ka at later stage glacio isostatic controlled incision was overruled due to high climate controlled sediment input from the catchment and probably initial glacio isostatic subsidence migration of channel belts towards the direction of the former centre of glacio isostatic uplift indicates that glacio isostacy influenced rhine meuse paleogeography until far into the lateglacial 2007 elsevier ltd all rights reserved

the high resolution holocene sea level curve for northwest germany global signals local effects or data artefacts a few years ago a new relative sea level curve for northwest germany was constructed for the entire german north sea coast it is characterised by several suspected sea level fluctuations to test this curve for local effects it was broken down into five relative sea level curves representative for five coastal sections the relative sea level curves were corrected for tidal effects and also a rough first correction for compaction was applied the five curves all differ from the original curve and from each other most of the suspected sea level fluctuations in the original curve cannot be supported and are discussed as data artefacts or local effects around ad 800 1000 all curves show stagnation or drop of sea level thus this signal is discussed as of over regional stratigraphic meaning this study is a first step 1 to show that several curves are needed to demonstrate the holocene sea level history of such a big area as the entire german north sea coast and 2 to establish reliable relative sea level curves for the german north sea coast further research is necessary to apply detailed corrections especially with respect to compaction prone data and to improve the individual curves

messinian subaerial erosion of the proto nile delta abstract the evaporitic drawdown and subsequent dessication of the mediterranean basins during the messinian salinity crisis has been confirmed by detailed seismic mapping of the ensuing erosion surface in the nile delta region the basal messinian unconformity determined by seismic analysis and borehole correlation extends from almost sea level in the southern delta area to depths of at least 5 km in the nile cone the onlap of the contemporaneously deposited fluvio deltaic clastics of the qawasim formation occurs at between 2 5 to 4 km below present gradual initial drawdown of the mediterranean sea with occasional sudden sporadic falls is implied by the presence of entrenched meanders and impaired rejuvenation terraces in the nile canyon formed as the proto nile river cut down into the pre existing tortonian delta complex the former tortonian delta slope became an extensive linear erosional front with over 3 km of vertical relief the uppermost levels of which were protected by tabular oligocene basalt flows preserved as mesas and buttes the lower slopes were the site of coalescing piedmont fans fed by upper slope wadi systems the piedmonts merged into the qawasim fluvio deltaic deposits of the proto nile fluvial flood plain the subcrop beneath the basal messinian unconformity reveals a remarkable diversity of rock type each with its own distinctive control on the geomorphology and geometry of the ensuing messinian erosional surface fracture patterns within the oligocene basalts produced a trellis drainage network which became later captured by a dendritic system developed on less resistant prodelta shales of the former tortonian delta slope close study of seismic profiles clearly demonstrates that the basal messinian erosional disconformity can be traced northwards to depths of at least 2 5 3 0 km before becoming affected by later pliocene faulting this validates a deep dessication model for the evolution of the messinian evaporites

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

chaotic breccia zones on the pembroke peninsula south wales evidence for collapse into voids along dilational faults chaotic breccias and megabreccias locally called gash breccias hosted within the pembroke limestone group visean mississippian lower carboniferous of southwest wales are re mapped along with spatially related crackle and mosaic breccias of thirteen studied megabreccia bodies seven lie along steep nnw or nne striking strike slip faults originating during north south variscan late carboniferous shortening though reactivated during later extension four bodies are conformable with e w striking steeply dipping bedding and two have irregular or indeterminate margins the bedding parallel zones are interpreted as the dilational tips of listric normal faults and the cross strike faults as transtensional transfer zones sub horizontal clast fabrics suggest brecciation by gravitational collapse into opening fissures rather than by cataclasis along the faults most fissures have geometrically matched margins produced by this dilational faulting and only locally have the indented margins indicating solutional processes the most likely age for the main fissure extension and fill is late triassic based on analogous dated fills at the eastern end of the bristol channel basin the pembroke megabreccias blur the distinction between fault rocks formed by deformation and those formed by redeposition along fault zones

cosmogenic nuclide dating of sahelanthropus tchadensis and australopithecus bahrelghazali mio pliocene hominids from chad ages were determined at two hominid localities from the chad basin in the djurab desert northern chad in the koro toro fossiliferous area kt 12 locality 16 00 n 18 53 e was the site of discovery of australopithecus bahrelghazali abel and in the toros menalla fossiliferous area tm 266 locality 16 15 n 17 29 e was the site of discovery of sahelanthropus tchadensis toumai at both localities the evolutive degree of the associated fossil mammal assemblages allowed a biochronological estimation of the hominid remains early pliocene 3 3 5 ma at kt 12 and late miocene 7 ma at tm 266 atmospheric 10be a cosmogenic nuclide was used to quasicontinuously date these sedimentary units the authigenic 10be 9be dating of a pelite relic within the sedimentary level containing abel yields an age of 3 58 0 27 ma that points to the contemporaneity of australopithecus bahrelghazali abel with australopithecus afarensis lucy the 28 10be 9be ages obtained within the anthracotheriid unit containing toumai bracket by absolute dating the age of sahelanthropus tchadensis to lie between 6 8 and 7 2 ma this chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock

the age origin and tectonic significance of mesozoic sediment filled fissures in the mendip hills sw england implications for extension models and jurassic sea level curves in the eastern mendip hills on the northern margin of the wessex basin sw england the carboniferous limestone is cut by numerous fissures that are filled with mesozoic sediments sedimentary dykes neptunian dykes the fissures contain a record of triassic lower jurassic sediments that are only sparingly preserved in their normal stratigraphical position between the carboniferous limestone and the unconformably overlying upper inferior oolite of bajocian age detailed analysis of cross cutting relationships facies analysis biostratigraphy lithostratigraphy and strontium isotope ages of relevant mesozoic sediments has allowed the construction of an upper triassic lower jurassic fissure fill stratigraphy for the eastern mendip area most fissures were clearly formed by rapid influx of unlithified sediment from the land surface or sea floor some smaller cavities or larger cavities with restricted access to the unconformity were apparently filled by sediment that trickled down into the fissure system the vast majority of the mendip fissures are interpreted as having formed as a response of the carboniferous limestone north of major basin bounding faults to pulses of tectonic extension during ladinian norian rhaetian late hettangian early sinemurian late sinemurian early pliensbachian late pliensbachian and bajocian times triassic earliest jurassic fissures have a broad spread of strike from e w to nw se to n s accommodating extension in a roughly ne sw direction younger jurassic fissures show well defined e w and n s trends with the former becoming dominant through time total extension of 4 7 n s and 0 6 e w was produced by the formation of triassic jurassic fissures within the carboniferous limestone such patterns of extension are thought likely to be characteristic of the subsurface geology in much of southern england and wales major implications of this study are that 1 the presence of seismically unresolvable sediment filled fissures in supposedly rigid fault blocks can lead to a significant underestimate of regional extension based on the restoration of motion on normal faults on seismic reflection profiles and 2 the isolation of pulses of tectonic activity with a temporal resolution of 10 5 10 6 years may provide a means of identifying a tectonic signal in relative sea level curves derived from the jurassic sedimentary record

decoding the origins of vertical land motions observed today at coasts in recent decades geodetic techniques have allowed detecting vertical land motions and sea level changes of a few millimetres per year based on measurements taken at the coast tide gauges on board of satellite platforms satellite altimetry or both global navigation satellite system here contemporary vertical land motions are analysed from january 1993 to july 2013 at 849 globally distributed coastal sites the vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic green s functions special attention is paid to the effects of glacial isostatic adjustment induced by past and present day ice melting various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally in well instrumented regions predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres residual vertical land motions show a strong local variability especially in the vicinity of plate boundaries due to the earthquake cycle significant residual signals are also observed at scales of a few hundred kilometres over nine well instrumented regions forming observation windows on unmodelled geophysical processes this study highlights the potential of our multitechnique database to detect geodynamical processes driven by anthropogenic influence surface mass changes surface loading and glacial isostatic adjustment and tectonic activity including the earthquake cycle sediment and volcanic loading as well as regional tectonic constraints future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models

basement reservoir plumbing fracture aperture length and topology analysis of the lewisian complex nw scotland upfaulted ridges of neoarchean crystalline basement rocks formed in the faeroe shetland basin as a consequence of mesozoic rift processes and are an active target for oil exploration we carried out a comprehensive fault and fracture attribute study on the extensive exposures of geologically equivalent crystalline basement rocks onshore in nw scotland lewisian gneiss complex as an analogue for the offshore oil and gas reservoirs of the uplifted rona ridge basement high our analysis shows a power law distribution for fracture sizes aperture and length with random to clustered spacing and high connectivity indices regional variations between the scottish mainland and the outer hebrides are recognized that compare directly with variations observed along the rona ridge in the faeroe shetland basin here we develop a model for the scaling properties of the fracture systems in which variations in the aperture attributes are a function of the depth of erosion beneath the top basement unconformity more generally the combination of size spatial and connectivity attributes we found in these basement highs demonstrates that they can form highly effective well plumbed reservoir systems in their own right supplementary material additional methods and results are available at https doi org 10 6084 m9 figshare c 5017139 thematic collection this article is part of the the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs

mn and fe rich black travertine shrubs bacterially and nanobacterially induced precipitates abstract black shrubs i e arborescent forms are present within hot water travertine deposits from morocco the shrubs are commonly a few centimeters high and laterally grouped along individual laminae other than in mineral composition the black shrubs closely resemble the calcite shrubs from other hot water travertine deposits e g bagni di tivoli italy and mammoth hot springs yellowstone national park they are composed of a variety of minerals that are mn rich and also have a significant fe oxide component similar mn and fe rich shrub like forms have been described from desert varnish deep sea mn nodules and marine carbonates frutexites sem analyses show that bacterial bodies are densely packed within the mn rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae the bacterial bodies range in shape and size from rods commonly 0 8 m long by 0 1 m in diameter to spherical forms commonly 0 3 m in diameter that form chains up to 1 m long to nanobacterial spheres 150 to 200 nm in diameter that make up densely packed chains commonly 15 m in length it is well documented within the microbiological literature that not only do bacteria have the ability to induce the precipitation of mn and fe they can concentrate mn in mineral precipitates from waters with very low to essentially undetectable concentrations of mn the black mn rich shrubs within the moroccan travertines other hot water travertines and related features such as desert varnish deep sea mn nodules and frutexites are postulated to also be the result of bacterially induced precipitation

geology and palaeontology of the upper miocene toros menalla hominid locality chad all six known specimens of the early hominid sahelanthropus tchadensis come from toros menalla site 266 tm 266 a single locality in the djurab desert northern chad central africa here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds the rich fauna from tm 266 includes a significant aquatic component such as fish crocodiles and amphibious mammals alongside animals associated with gallery forest and savannah such as primates rodents elephants equids and bovids the fauna suggests a biochronological age between 6 and 7 million years taken together with the sedimentological evidence the fauna suggests that s tchadensis lived close to a lake but not far from a sandy desert perhaps the oldest record of desert conditions in the neogene of northern central africa

fishes and palaeogeography of the african drainage basins relationships between chad and neighbouring basins throughout the mio pliocene article i nfo keywords miocene pliocene palaeobiogeography africa the neogene african fossil record of two fishes i e semlikiichthys perciformes indet and calarius siluriformes ariidae is reviewed including new material from chadian outcrops their distribution confirms the existence of a nilo sudan ichthyological province during an early part of the miocene an east west waterway is demonstrated to have crossed africa allopatric speciation in the chadian and east african areas suggests that a split occurred in this system prior to 7 ma moreover our data support the existence of hydrographical connections between the chadian basin and the syrte basin after 7 ma at about the mio pliocene boundary finally our study also demonstrates that connections between the niger and chad basins

long term salt marsh vertical accretion in a tidal bay with reduced sediment supply abstract because of damming and intensive human activities the sediment supply to many estuaries and deltas is dramatically decreasing in the oosterschelde southwest netherlands a storm surge barrier ssb and two compartmentalization dams were built in the 1980s to protect the densely inhabited inland against flooding after these constructions the tidal range and mean high water level in the oosterschelde decreased by about 12 and suspended sediment concentrations in the channels dropped by 52 70 compared to the pre barrier conditions the vertical accretion rates of the three largest salt marshes rattekaai sint annaland and slaak in the oosterschelde in response to this decreased sediment supply were investigated there was a general accreting trend over the entire post barrier period 1988 2011 in all three marshes the predicted slowdown in accretion rates by de jong et al 1994 did not persist although accretion rates were lower than in the pre barrier period more than 20 year observations from kaoline markers showed variation of accretion rates within and among marshes year to year variation in accretion rates was large but only weakly not significantly related to the duration and frequency of marsh overflow and over marsh extreme flooding events however storm events are hypothesized to be responsible for the observed trends but our observations lack the temporal resolution to identify specific storm events salt marshes in the oosterschelde are expected to survive under the present sea level rise rate and subsidence rate scenarios

fissure fills along faults variscan examples from gower south wales the extent to which persistent rather than transient fissures wide planar voids can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon bearing fluids variscan late carboniferous faults cutting dinantian lower carboniferous limestones on the gower peninsula south wales host clear evidence for fissures up to several metres wide evidence includes dendritic hematite growth and elongate calcite growth into open voids spar ball and cockade breccia formation laminated sediment infill and void collapse breccias detailed mapping reveals cross cutting geometries and brecciation of earlier fissure fills showing that fissures were formed during rather than after active faulting fissures therefore probably formed by geometric mismatch between displaced fault walls rather than by solution widening along inactive faults

clumped isotope evidence for episodic rapid flow of fluids in a mineralized fault system in the peak district uk we have used clumped isotope thermometry to study a fault hosted hydrothermal calcite vein associated with the mississippi valley type mvt mineralization on the derbyshire platform in the southern pennines uk this is the first published dataset obtained using a new mass spectrometer mira optimized for clumped isotope analysis and an associated clumped isotope temperature calibration we analysed multiple generations of vein growth at high spatial resolution in two transects across the vein the vein grew episodically at temperatures between 40 and 100 c we interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures heat is conserved in the fluid as it ascends along the fault surface and thus flow must have been fast and restricted to short lived pulses the flux could have been driven by high pore pressures associated with rapid sedimentation hydrocarbon generation and diagenesis in the basinal facies of the visean bowland hodder group natural hydraulic fracturing of shale units and failure of capillary seals possibly triggered by uplift allowed the release of fluids into aquifers within the sediment pile the transmission of high pore fluid pressures from the shales to the fault zone aided by the compressibility of the gas phase in two phase pore fluids may have resulted in fault rupture accompanied by enhanced fracture permeability and rapid fluid flow vein growth ceased as pore pressures dissipated such behaviour is closely related to a seismic valve type model for mineralization supplementary material details of the methods and equipment are available at https dx doi org 10 6084 m9 figshare 3808329 v9

genesis of cockade breccias in the tectonic evolution of the cirotan epithermal gold system west java the pliocene cirotan gold deposit provides an exceptional example of mineralized breccias and in particular cockade breccias analysis of these breccias approached through both field observation and image analysis on photographs made it possible to determine their method of graded formation the mineralized structure as much a 25 m thick in places is a right lateral strike slip fault that evolved to a normal fault at the end of the system s development it consists of juxtaposed breccia bodies separated by major slip or septa which formed at a major inflection of the host fault the breccia bodies all show a similar internal organization from footwall to hanging wall one passes from a siliceous breccia with angular clasts to a thick infill of cockade breccia showing a reverse grading with small centimetre size cockades aspect ratios of 1 10 passing to larger up to 1 m more equant cockades aspect ratios 1 3 in contact with the hanging wall the different stages of cockade formation demonst

crack seal microstructure evolution in bi mineralic quartz chlorite veins in shales and siltstones from the rwth 1 well aachen germany abstract in core samples from the deep geothermal well rwth 1 we studied variscan quartz chlorite veins formed by crack seal processes in siliciclastics at the brittle to ductile transition these sheared veins are common in sections of the well which are interpreted as variscan thrust zones based on image logs and seismic data microstructures interpreted to reflect different stages in the evolution of such crack seal veins suggest the veins started in microcracks sealed by quartz and chlorite to veinlets crossing multiple grains and bundles of veinlets evolving by progressive localization into low angle extensional shear veins and high angle dilational jog veins in the sheared veins chlorite and quartz ribbons show evidence for crack seal and simultaneous ductile shearing during vein evolution forming peculiar fin shaped microstructures in quartz ribbons in high angle dilational jogs fibrous crystals of quartz and chlorite point to multiple crack seal events with simultaneous growth of two different mineral phases this is interpreted to be the basic microstructural process in the veins we extend earlier models of polycrystal growth in fractures and present a series of 2d simulations of the kinematics of crystal growth in these bi mineralic veins for both localized and non localized cracking results are compared with the observed microstructures we show that when the relative growth rates of the two mineral phases are different serrated grain boundaries evolve the similarities between observation and model suggest that the assumption of our model is valid although many second order processes require a more detailed study we propose that the principles observed here can be applied to other bi mineralic crack seal veins

quantifying fault breccia geometry dent fault nw england a geometric classification of fault breccia borrowed from the cave collapse literature has been suggested as an alternative to available genetic classifications here image analysis is used to explore geometric discrimination between the visually assigned classes of crackle breccia mosaic breccia and chaotic breccia using samples from the well understood dent fault northwest england clast sphericity and surface roughness show some correlation with the breccia classes but particle size distributions and their fractal dimension show none a more useful parameter is the percentage of sample area occupied by clasts crackle breccia has 75 clasts mosaic breccia 60 75 clasts and chaotic breccia has 60 clasts the eye is also good at judging the tessellation goodness of fit of clasts and a semi quantitative approach to assessing this parameter is explored the average degree of rotational misfit of the clasts is strongly related to breccia class crackle breccia involves less than 10 average rotation mosaic breccia 10 20 and chaotic breccia more than 20 rotation comparison charts are provided for semi quantitative classification of fault breccias

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

the mediterranean hydrologic budget from a late miocene global climate simulation during the late miocene the mediterranean experienced a period of extreme salinity fluctuations known as the messinian salinity crisis msc the causes of these high amplitude changes in salinity are not fully understood but are thought to be the result of restriction of flow between the mediterranean and atlantic eustatic sea level change and climate results from a new atmospheric general circulation model agcm simulation of late miocene climate for the mediterranean and adjacent regions are presented here the model hadam3 was forced by a late miocene global palaeogeography higher co2 concentrations and prescribed sea surface temperatures the results show that fluvial freshwater fluxes to the mediterranean in the late miocene were around 3 times greater than for the present day most of this water was derived from north african rivers which fed the eastern mediterranean this increase in runoff arises from a northward shift in the intertropical convergence zone caused by a reduced latitudinal gradient in global sea surface temperatures the northwards drainage of the late miocene chad basin also contributes numerical models designed to explore late miocene salt precipitation regimes in the mediterranean which typically make use of river discharge fluxes within a few tens of percent of present day values may therefore be grossly underestimating these fluxes although the agcm simulated late miocene river discharge is high the model predicts a smaller net hydrologic budget river discharge plus precipitation minus evaporation than for present day we discuss a possible mechanism by which this change in the hydrologic budget coupled with a reduced connection between the mediterranean and the global ocean could cause the salinity fluctuations of the msc

aridity and humidity two aspects of the late miocene climate of north africa and the mediterranean abstract the physiography of north africa is not greatly changed from that of the messinian with the drawdown of the mediterranean in the late messinian the then existing river systems were incised into the landscape and emptied into lake cyrenaica which occupied the substantially drained eastern mediterranean basin the record of incision provides a record of the magnitude of the messinian river systems an analysis of these river systems demonstrates that messinian rainfall a consequence of the zeit wet phase was greatest in east and south central north africa in keeping with the derivation of the water mainly from the indian ocean in central north africa the eosahabi river flowed from messinian lake chad eroding the east tibesti valley and cutting a channel which is especially well preserved near the coast of the gulf of sirt the penetrated sediments of lake cyrenaica and the marginal basins of the messinian transgression are known as the upper evaporites and are generally fine clastics gypsarenites and gypsum anhydrite they were rapidly deposited underlying them is the halite of the lower evaporites this sequence of upper and lower evaporites is much like the lower halite of the tortonian south gharib formation and the overlying clastics and anhydrite of the messinian zeit formation in the gulf of suez red sea area this type of sequence is termed an evaporitic couplet and as has been demonstrated for the gulf of suez red sea is a consequence of a transition from a dry to a more humid climate in a restricted or semirestricted basin this transition occurred at about 7 5 ma in the gulf of suez red sea and at about 5 8 ma in the mediterranean the zeit wet phase manifest in the above events developed in association with the initiation and development of the asian monsoon and the drying of the mediterranean it can be understood in terms of the development of an evolving monsoon desert system the asian monsoon was initiated 8 7 ma in association with the uplift of tibet at this time the north african desert zone was displaced northwards to be over the mediterranean and central and eastern north africa became seasonally humid a concept is advanced in which the early stage of the development of the asian monsoon is seen as having two phases alternating at the precessional ca 21 ka cycle one phase transferred moisture from the indian ocean mainly to southern asia the other phase transferred moisture mainly to north africa with the drawdown of the mediterranean at about 5 8 ma the zeit wet phase intensified a further northward movement of the humid and desert zones occurred at the time of drawdown with the messinian and early pliocene transgressions the wet phase ameliorated but a substantial river system still crossed central north africa at about 4 6 ma north africa became drier probably in response to the developing dominance of the features of the monsoon that transferred moisture mainly to southern asia features of the monsoon that are well recognised today

structural controls and origin of gold silver mineralization in the grampian terrane of scotland and ireland gold bearing mineral deposits occur over a strike distance of 300 km within the grampian terrane of scotland and ireland this terrane consists of neoproterozoic lower ordovician rocks of the dalradian supergroup that were polyphase deformed and metamorphosed during the c 470 ma grampian orogeny sulphide rich au ag deposits occur in scotland at calliachar urlar burn tombuie tyndrum and cononish and in ireland at curraghinalt omagh cavanacaw croagh patrick cregganbaun and bohaun they are hosted by 0 1 6 m thick quartz veins and have a similar overall mineralogy including native gold as cu fe pb and sn sulphides with hessite tetrahedrite and electrum present in the first six localities above the mineralized quartz veins which are characterized by open space textures crystallized at c 3 5 km depth in the crust all of the deposits were structurally controlled and apart from curraghinalt occur within second order riedel r r and t fractures resulting from a regional n s trending maximum principal stress these deposits are of upper silurian to lower devonian post scandian age and are inferred to have crystallized from hot silica rich metamorphic fluids derived from dehydration reactions at the greenschist amphibolite facies boundary curraghinalt is an older grampian thrust related deposit plutonic igneous rocks mainly granitoid contributed in part to the fluids which were channelled into major orogen parallel strike slip faults to be injected by fault valve pumping into the damage zones and fault breccias of newly formed riedel fractures any residual fluid probably percolated to the ground surface to form rhynie chert type hot springs

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

automatic inference of ice models from postglacial sea level observations theory and application to the british isles late pleistocene and holocene sea level change is caused mostly by melting of ice sheets since the last glacial maximum and the earth s delayed uplift in response to changes in the surface load records of sea level change therefore contain information on earth rheology and ice sheet history and have been used to constrain ice and earth models a method is presented which finds an ice model that simultaneously fits the sea level record and the constraints on ice elevation it infers the ice model which maximizes the smoothness of the surface and thus produces realistic ice models with the minimum detail required to fit the observations this is a significant improvement on previous work in which the ice model was iteratively improved by ad hoc adjustments resulting in a model that is dependent on the initial model the method is applied to the british isles and a model with a spatial resolution of 50 km and temporal resolution of 1000 years is obtained for the late glacial period glaciological data determining the maximum elevation of the ice provide an important constraint on the model as does information on the timing of formation of such trimline data it is possible to infer ice volumes up to a few thousand years before the earliest sea level data and therefore the availability of early sea level data is most important to constraining ice models for the time of maximum glaciation

a seismodynamical model of lithosphere deformation development of continental and oceanic rift networks seismicity and lithosphere extension on the scale of a tectonic plate are investigated in two horizontal dimensions and time using a dynamical model for a thin plate overlying a viscoelastic channel the plate consists of two layers a brittle elastic plastic crust that deforms as a result of earthquakes along faults and a strong viscoelastic layer representing the aseismic creeping lower lithosphere numerical experiments of lithosphere rifting are performed for one and two layer lithosphere models using two different rupture criteria in all the calculations earthquakes and faults of various sizes may form anywhere in the numerical domain as a result of the constitutive formulation the differences between the one and two layer model results suggest a mechanical explanation for the difference between continental and oceanic rifting when the lower lithosphere is absent a small number of faults dominate the deformation and a relatively simple narrow rift zone develops corresponding to oceanic rifting when a highly viscous lower lithosphere is included a complex distributed network of faults develops similar to continental rifting the complexity of the fault system also depends on the yield criterion in the crustal layer in our simulations complexity is greater for a yield criterion with strong shear stress dependence than for one with mainly extensional stress dependence whether a result of lower lithosphere stretching crustal heterogeneity or the yield criterion higher complexity increases the timescale for fault development increases self similarity in fault system geometry and stress and strain time series and results in power law moment frequency earthquake size scaling

precessional variability of 87 sr 86 sr in the late miocene sorbas basin an interdisciplinary study of drivers of interbasin exchange we present the first subprecessional record of seawater 87sr 86sr isotope ratios for a marginal mediterranean subbasin the sediments contained in this interval three precessional cycles between 6 60 and 6 55 ma are important because they record conditions during the transition to the messinian salinity crisis msc 5 97 to 5 33 ma an event for which many details are still poorly understood the record derived from planktic foraminifera of the late miocene sorbas basin se spain shows brief excursions with precessional cyclicity to 87sr 86sr ratios higher than coeval ocean 87sr 86sr the hydrologic conditions required to generate the observed record are investigated using box modeling constrained using a new paleodepth estimate 150 to 250 m based on benthic foraminiferal assemblages the box model results highlight the role of climate driven interbasin density contrast as a significant driver of or impediment to exchange the results are particularly significant in the context of the msc where 87sr 86sr excursions have been interpreted purely as a consequence of physical restriction to replicate the observed temporal patterns of lithological variations and 87sr 86sr isotope excursions the sorbas basin box must have a mainly positive hydrologic budget in contrast with the mediterranean s negative budget during the late miocene this result has implications for the assumption of synchronous deposition of specific sedimentary layers sapropels between marginal and open mediterranean settings at subprecessional resolution a net positive hydrologic budget in marginal mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits

gravity anomalies and flexure of the lithosphere at the middle amazon basin brazil the middle amazon basin is a large paleozoic sedimentary basin on the amazonian craton in south america it contains up to 7 km of mainly shallow water sediments a chain of bouguer gravity highs of approximately 40 to 90 mgals transects the basin roughly coincident with the axis of maximum thickness of sediment the gravity highs are flanked on either side by gravity lows of approximately 40 mgals the observed gravity anomalies can be explained by a steeply sided zone of high density in the lower crust varying in width from 100 to 200 km wide within this region the continental crust has been intruded replaced by more dense material to more than half its original thickness of 45 50 km the much wider sedimentary basin results from regional compensation of the subsurface load and the subsequent load of accumulated sediments by flexure of the lithosphere the observed geometry of the basin is consistent with an elastic lithosphere model with a mechanical thickness of 15 20 kin although this value is lower than expected for a stable cratonic region of early proterozoic age it is within the accepted range of effective elastic thicknesses for the earth rapid subsidence during the late paleozoic may be evidence of a second tectonic event or lithospheric relaxation which could lower the effective mechanical thickness of the lithosphere the high density zone in the lower crust as delineated by gravity and flexural modeling has a complex sinuous geometry which is narrow and south of the axis of maximum sediment thickness on the east and west margins and wide and offset to the north in the center of the basin the linear trough geometry of the basin itself is a result of smoothing by regional compensation of the load in the lower crust

reconciling geodetic and geological rates of vertical crustal motion in intraplate regions abstract tectonic motion rates of individual faults and regional deformation in an intraplate setting are estimated based on the analysis of ten yearly surveys of a regional levelling network in ne ardenne w europe owing to the frequency and number of measurement epochs much greater than in classical comparisons of general surveys the tectonic and near surface components of ground motion are clearly separated the marked temporal variability in ground motion strongly depends on the amount of precipitation fallen during the six months preceding each survey and the subsequent drying off of the subsoil at the time of the surveys moreover the ground response to this influence varies from place to place leading to high differential movements at the local scale taking into account the percentage of surveyed faults which moved tectonically during the time of the study i calculate fault motion rates of 0 06 0 09 mm yr similar to geological rates moreover the data indicate that one way for intraplate normal faults to accommodate tectonic strain aseismically is intermittent fault creep with short episodes of a few mm displacement separated by many year long time intervals of fault quiescence a flexural deformation shows the superposition of a tilt event on a trend corresponding to a tilt rate of 0 16 rad yr for a 2 8 km long segment

late quaternary sea level change and isostatic and tectonic land movements along the belgian dutch north sea coast geological data and model results early and middle holocene sea level data from belgium plot ca 2 m above data from the western netherlands reflecting differential tectonic and isostatic movements the total uplift rate of belgium relative to the western netherlands decays gradually from 0 66 m kyr 1 at 7500 cal yr bp to less than 0 25 m kyr 1 since 5000 cal yr bp the tectonic component of this relative movement inferred from eemian sea level data is in the order of 0 06 to 0 16 m kyr 1 the isostatic component of the uplift is related to the last phase of the collapse of a peripheral bulge under the netherlands and the dutch and german sectors of the north sea and to hydroisostatic subsidence of the north sea basin caused by water loading as sea level rose comparisons with isostatic rebound models show that they predict well the holocene isostatic movement between belgium and the western netherlands and that the predictions are improved when the tectonic component is removed from the observations preliminary evaluation of sea level data from the dutch sector of the north sea shows that glacio hydroisostatic subsidence relative to belgium was significantly greater than for the western netherlands coastal area and spatially highly variable copyright 2002 john wiley sons ltd

modeling the subsidence of peat soils in the dutch coastal area in large parts of the western coastal region of the netherlands peat soils occur historic land use resulted in decomposition of organic matter and compaction of these soils and as a consequence the land surface subsided along with sea level rise and tectonic subsidence since the end of the weichselian ice age this resulted in a country where one third of the land lies below mean sea level global warming will accelerate the sea level rise and land subsidence due to peat oxidation leading to elevated risks of flooding and increasing upward seepage of brackish and nutrient rich ground water in the polder groot mijdrecht near amsterdam the land surface is currently between 5 and 6 5 m below sea level for this polder we calibrated a model for the land surface subsidence the subsidence rate is modeled using a differential equation accounting for the peat oxidation and other processes causing land surface subsidence the model input consists of information on i the thickness of peat layers derived from soil surveys in 1964 and 1967 ii the regulated surface water levels in a network of drainage ditches and iii the initial elevation measured between 1954 and 1968 at 1423 locations the model was calibrated on the elevation measurements in 2005 and on the peat thickness from a recent soil survey in 2005 the subsidence between 1954 and 2005 as predicted with the model was validated with a subsample of 100 points out of the 1423 locations the average rate of predicted subsidence between 1954 and 2005 was approximately 5 mm year 1 in soils containing peat layers the predicted subsidence rate due to peat oxidation was up to 8 mm year 1 on the contrary at locations without peat the predicted subsidence rate was only 0 7 mm year 1 the model accounted for 78 of the variance of the historic subsidence and the root mean squared error of the predicted elevation in 2005 was 94 mm model forecasts of the cumulative subsidence between 2005 and 2020 for the eastern half of the study area where still thick peat layers occur were over 80 cm in areas where peat layer in the soil profile are absent the forecasted cumulative subsidence was 10 mm the case study shows that the simple process model when calibrated on local data can help in evaluating flooding risks and in taking long term strategic decisions on water management and land use in peat areas

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

slip tendency analysis as a tool to constrain fault reactivation a numerical approach applied to three dimensional fault models in the roer valley rift system southeast netherlands we describe a new numerical approach to constrain the three dimensional 3 d pattern of fault reactivation taking advantage of the knowledge of the tectonic stress field the ratio of the resolved shear and normal stresses slip tendency as well as the direction of the shear stress is calculated at every location on the faults modelled by triangulated surfaces although the calculated contact stresses represent only a first order approximation of the real stresses comparison of the 3 d pattern of slip tendency with the frictional resistance of the fault can provide useful constraints on the probability of fault reactivation the method was applied to 3 d geometrical fault models in the roer valley rift system southeast netherlands which is presently characterized by pronounced tectonic activity the input stress tensors were constrained by published stress indicators the analysis demonstrated that the observed fault activity could be explained within a reasonable range of frictional parameters and input stress magnitudes in addition a fairly good correlation was found between the predicted slip directions and the focal mechanisms of local earthquakes this suggests that in the study area fault models being valid in the uppermost part of the crust are suitable to constrain fault reactivation even in the deeper part of the seismogenic layer the analysis further demonstrated that fault hierarchy and the regional tectonic contexts of the fault system are important factors in fault reactivation therefore they always should be taken into account during evaluation of the calculated slip tendency and slip direction patterns

late quaternary evolution of the feldbiss fault roer valley rift system the netherlands based on trenching and its potential relation to glacial unloading abstract the most important tectonic structure in the southern part of the netherlands is the roer valley rift system rvrs the main border fault zones of the rvrs the peel boundary and the feldbiss fault zones have been active during the quaternary and are still active today as indicated by the occurrence of earthquakes in this paper we present the results of a trench across the feldbiss fault part of the feldbiss fault zone this trench provided no evidence for earthquakes along this segment of the fault zone fluidization structures were not encountered a sudden increase in the average fault displacement rate was inferred for the period around 15 ka b p in a trench nearby across the geleen fault of the same fault zone the limited age control cannot exclude that such an acceleration also occurred at the feldbiss fault during the second half of the 1990 s several paleoseismological trenching studies have been carried out in the rvrs the compilation of the results of these studies reveals that the main border faults possibly experienced an increase in fault activity around 10 15 ka b p the timing of this increased activity and results from glacial rebound modelling indicate that glacial unloading of the crust can have triggered this increase in fault activity

seamount loading and stress in the ocean lithosphere 2 viscoelastic and elastic viscoelastic models analytical solutions are presented for the deformation and stress state of a horizontally stratified earth subject to normal loads of size and wavelength that are characteristic of seamounts the models investigated include layered elastic plates homogeneous viscoelastic plates and elastic over viscoelastic models in all cases the composite models overlie an inviscid half space the principal advantage of the laminated elastic models over homogeneous elastic plates is that they can result in a substantial reduction in the maximum stress differences in those parts of the plate least capable of supporting large stress differences authors

neotectonics of the netherlands a review abstract earthquakes and vertical land movements inferred from geodetic levelling results demonstrate that the netherlands is situated on a tectonically active part of the earth s surface tectonic subsidence analyses of the sedimentary records in the basins and the history of tectonic uplift inferred from meuse river terraces show that the current tectonic activity is part of a deformation phase which began in the late early miocene which we take as the start of the neotectonic period the neotectonic faulting mode is normal slip this is in accordance with the present day orientation of the maximum horizontal stress and the vertical orientation of the maximum stress however the neotectonic fault zones are reactivated variscan or older wrench faults these faults have been reactivated repeatedly during the mesozoic and cenozoic in normal and wrenching modes and therefore represent fundamental crustal weakness zones as a result the surficial neotectonic fault pattern resembles the inherited wrenching fault pattern although the faulting mode is normal slip this is illustrated for the area where normal faults have displaced the meuse fluvial terrace system in the southeastern part of the netherlands the neotectonic vertical motions in and around the roer valley rift system have affected the courses of the rhine and meuse rivers from pliocene times until the present in addition a fluvial terrace staircase developed along the meuse river in response to the uplift of the ardennes rhenish massif and its foreland for example near maastricht furthermore small fault scarps are present along segments of the bounding fault zones of the roer valley graben the peel boundary fault zone and the feldbiss fault zone in other parts of the netherlands the neotectonic vertical motions have no direct expression in the morphology examples of possible indirect control on the morphology in these areas occur in glacial landscapes the zuiderzee basin and the coastal zone

shear zones as a new type of palaeostress indicator this paper proposes that shear zones act as palaeostress indicators in much the same way as brittle faults several hundred shear zones from both the limbs of the variscan langland mumblcs anticline south wales are treated using the graphical and numerical methods of fault slip analysis estimated palaeostress directions derived from shear zones are characterized by greater scatter than where brittle faults are used as stress indicators an important reason for this is the fact that on some shear zones the direction of maximum shear stress slip lineation is not perpendicular to the line of s c intersection as a consequence the use of slip lineations produces better solutions than cases where the slip direction is inferred as a line perpendicular to the s c intersection the filtering of data to reduce the scatter in the results produces insignificant improvement and is considered unnecessary

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

the late neogene sahabi rivers of the sahara and the hamadas of the eastern libya chad border area abstract this paper contributes to the concept that during the late tortonian messinian and early pliocene c 7 5 4 6 ma in addition to the nile the sahabi rivers also crossed the sahara having originated from tropical neogene lake chad examination of two hamadas lying just to the north of the libya chad border using landsat images and srtm topographic data enables one of them hamada ibn battutah west to be recognised as an uplifted palaeosurface which preserves late miocene early pliocene fluvial activity this surface is referred to as the yangara palaeosurface of particular interest on the hamada are two long c 50 km wide c 4 km channels a 50 km 2 relic landscape and a short well defined 5 km channel about 1 km wide the location of hamada ibn battutah west is significant because the hamada provides evidence of extensive fluvial activity part way between the place of origin of the sahabi rivers and their preserved record at the gulf of sirt the yangara palaeosurface is considered to extend southwards to the adjacent hamada in northeastern chad the total palaeosurface extends 165 km in an approximate north south direction and averages 45 km in width it lies in the central part of an area of complex post miocene uplift involving four hamadas at the libya chad border

quantitative analysis of north sea subsidence stratigraphic and geophysical maps of the northern and southern north sea basin are used to study mechanisms of intracratonic basin formation these maps include 1 tectonic subsidence for ten stratigraphic units 2 predicted and observed sediment overpressure 3 geographic variation of compaction constants 4 net basement fault extension 5 free air gravity 6 flexural rigidity 7 heat flow and 8 predicted hydrocarbon maturation in northern areas of the north sea observed basement fault extension crustal thinning present day flexural rigidity and tectonic subsidence are predicted reasonably well by a simple stretching model of basin formation with rifting phases during the triassic and mid jurassic early cretaceous in southern areas of the north sea however a similar analysis suggests that other non extensional rift related processes dominated basin evolution the effects of anomalously active aesthenospheric convection coupled with basalt eclogite and deep crustal dewatering reactions are considered as possible additional mechanisms the troughlike form of quaternary tectonic subsidence suggests a new phase of rifting may be starting in the north sea the importance of such thermal rejuvenation is borne out by the association of areas of differential subsidence with high heat flow and low flexural rigidity one component of tectonic reactivation during this period may be due to thermally induced isostatic reequilibration of older tectonic loads

tectonic vs shallow origin of geodetically inferred ground movements an ne ardenne belgium case in order to get a better insight into the temporal pattern of height change variations in a moderately seismic intraplate area a 1 km long section has been weekly leveled from april 21 1997 to january 12 1998 in ne ardenne belgium as this section is located very close to a small reservoir of 25u10 6 m 3 it also allowed the influence of lake level variations on the nearby ground motion to be studied the measured height difference variations show a maximum amplitude of 3 45 mm with weekly values not exceeding 1 mm a two dimensional 2d finite element modeling confirms that waterload variations in the lake are the primary cause of movement of the section inducing maximum ground subsidence of about 2 cm and seasonal tilting of 3 4 wrads within a range of 2 3 km we also show that a fault passively alters the spatial distribution of the waterload dependent movements the removal of this component from the observed ground motion leaves oscillating residual displacements characterized by an amplitude of 1 1 5 mm and a period of about 2 months we demonstrate that these displacements are independent of rainfall and probably of groundwater fluctuation too although most of the residual motions take place on the fault straddled by the leveling section no credible mechanism can be found to ascribe these motions to a tectonic process fl 2000 elsevier science b v all rights reserved

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

global sea level change determination and interpretation the notion of sea level rise brings to the popular mind the specter of deep inundation of coastal regions one pictures skyscrapers emerging from the waters like so many sleeping flamingos standing in the shallows of a lake of course if all of the world s ice sheets suddenly melted or collapsed this vision would apply to new york city and its coastal counterparts but there is a general consensus that such a calamity is not an immediate threat houghton et al 1990 the actual situation for the recent historical past and near future appears to be more benign but with nonetheless extremely significant even devastating impacts due to erosion and flooding of coastal areas

interactions between fluvial and eolian geomorphic systems and processes examples from the sahara and australia abstract the remains of once integrated drainage systems are still discernible in many of the hot deserts of the world some of these date back to the mesozoic as in arid western australia where they now form chains of salt lakes others were active in miocene times such as the sahabi rivers that once flowed from chad to the mediterranean a few remained active during quaternary interglacials as in the sahara all contributed sediments that were reworked by wind during drier phases to form desert dunes the desert dunes of australia and of the 9500 km long chain of deserts extending from the sahara through arabia to the thar desert of india originated from sediments eroded from the uplands and deposited in closed interior basins formed during the course of late mesozoic and cenozoic faulting rifting and epeirogenic movements it was the unconsolidated neogene sediments laid down in large subsiding sedimentary basins such as the kufra sirte basin in libya and the chad basin which provided the source material for the late pliocene and quaternary desert dunes of the sahara one effect of the progressive build up of high latitude ice sheets during the neogene was to steepen the temperature and pressure gradients between the equator and the poles resulting in increased trade wind velocities stronger winds were better able to mobilize the alluvial sands of the increasingly dry sahara and adjacent deserts and to fashion them into desert dunes a more subtle form of interaction between eolian and fluvial processes concerns the interplay between desert dust loess accumulation on hill slopes in arid regions and the onset of fine grained valley fill accumulation by sluggish low energy streams in mountain valleys some of these late pleistocene wetlands served as refuge areas for plants reptiles and invertebrates at a time when the surrounding desert plains were very cold and dry as in the flinders ranges of south australia in the arid flinders ranges such valley fills were built up between 35 kyr and 15 kyr ago after which the return of the summer monsoon led to stream channel incision and the formation of a network of gullies often erroneously attributed to human activities understanding the causes of such accelerated erosion can prevent unnecessary and expensive attempts at restoration since the latter are based on the incorrect assumption that overgrazing and present day land use are responsible

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

linking short timescale deformation to long timescale tectonics one of the great successes of plate tectonics has been to provide a link between deformations of the lithosphere observed over widely varying timescales for example the slip between two plates as measured from young magnetic anomalies and hence averaged over the past 1 2 myr has been found1 3to be compatible with estimates obtained from slip during recent earthquakes despite the small time interval covered by the earthquake observations here we start from the idea4 5 that geological deformations are the long term cumulative trace of short term processes such as earthquakes so that the latter can be described as a high frequency noise for the former we return to a theoretical framework6 introduced to model large scale and long term tectonics based on a nonlinear diffusion equation but here explicitly associate the noise term with earthquakes the observed power law relationship between earthquake frequency and magnitude together with an assumption that strain is on average scale independent leads to the prediction that the largest earthquakes will have a gutenberg richter b value of 1 5 as has recently been reported for large mw 7 earthquakes worldwide7

lithospheric dynamics and the rapid pliocene quaternary subsidence phase in the southern north sea basin abstract we present stratigraphic modeling and quantitative analysis of the pliocene and quaternary subsidence of the southern north sea basin during the late pliocene well before the onset of quaternary glaciation the subsidence rate in the southern part of the north sea basin showed a ten fold increase relative to previous tertiary rates the high pliocene quaternary subsidence rate is consistent with the direction and state of the present intraplate stress field in northwest europe one possible consequence of the modern compressional stress field in northwest europe is reactivation of faulting in the central graben resulting in localized stretching and the development of pull apart basins alternatively the acceleration in late pliocene subsidence rates could be due to localized flexural downwarping of the lithosphere in the central graben caused by an increase in the level of intraplate compression both mechanisms succesfully predict the major characteristics of the overall quaternary subsidence history and stratigraphy gravity modeling suggests that the mechanism of localized stretching dominates the recent tectonostratigraphic evolution of the southern north sea

holocene sea level database for the rhine meuse delta the netherlands implications for the pre 8 2 ka sea level jump abstract this paper provides the most accurate sea level index points slips for the rhine meuse delta rmd the netherlands identified amidst a wealth of data accumulated in sixty years of research following documented protocols 106 selected radiocarbon dates from peat beds from transgressed valley floor upper estuarine and back barrier lagoonal settings were first listed individually then screened in ensemble on quantified age depth position and inshore palaeotidal setting the database contains 50 slips and 56 upper limiting data points spanning a depth range of 34 to 1 5 m the dates in the database originate from dedicated sea level research which kept surface elevation and sampling depth uncertainty small and sampling of basal peat beds was favoured keeping compaction uncertainties small too the slips cover an age range of 8 8 3 0 ka bp and are available from greater rotterdam and its near offshore for upper limiting data points the coverage extends offshore tracing the rhine palaeovalley and reaches back to 11 5 ka bp the age depth data density and spatial concentration of subsets of dates allow to perform bayesian radiocarbon calibration and to reduce temporal uncertainty by 25 for the average sample 1 age uncertainty 75 cal yr when depth position and rates of relative sea level rise rslr are used to assign sequence order between 8 0 4 5 ka bp rates of rslr gradually decreased from 9 to 1 mm yr in the millennium before rates of rslr were much higher on average 10 mm yr and marked by a sea level jump between 8 45 8 2 ka bp a two phased nature of this jump starts to be resolved with local magnitudes of 1 7 0 6 m 1 first phase and 0 2 0 2 m second phase corresponding to globally averaged jumps of 2 5 m 0 9 m for the first and 0 3 0 3 m for the second phase for the pre 9 ka bp period only offshore upper limiting data points are currently available until new offshore data are gathered trends of rslr before 9 ka bp can only be estimated fed with global insights in post glacial eustasy regional estimates regarding rates of glacio isostatic adjustments and tectonic subsidence and sedimentary geological interpretations of scattered basal peat presence

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

the nature and significance of rift related near surface fissure fill networks in fractured carbonates below regional unconformities fissure fill networks are a widely recognized but relatively little described near surface phenomenon supplementary material appendix a is available at https doi org 10 6084 m9 figshare c 5023103

geological causes of recent 100 yr vertical land movement in the netherlands abstract geodetic levelling data record differential vertical movements of the top of the pleistocene sands of up to 1 5 mm year in the netherlands over the last century we compare these movements to a mean tectonic isostatic and compaction movements at time scales of millions of years obtained by backstripping of cenozoic stratigraphy and b estimates of recent 100 yr movements from process modelling of isostasy glacio and hydro isostasy and compaction the process rates at time scales of millions of years are insufficient to account for the geodetic observations by an order of magnitude the isostasy and compaction rates inferred for the last century are also insufficient they explain less than half of the observed movements this suggests that the residual observed rates less isostasy and compaction estimates which is interpreted to represent tectonic crustal deformation constitutes an important contribution to present day movements the surprisingly high rates of short term tectonic vertical movements in a region which is relatively inactive seismically indicate that correction of tide gauge records for the glacio isostatic signal alone does not yield an appropriate measure of eustatic sea level rise along the dutch coast

gps monitoring of vertical ground motion in northern ardenne eifel five campaigns 1999 2003 of the hard project we present the hard project of gps monitoring of vertical ground motion in ne ardenne and eifel western europe its main purposes are to get a better insight into the present day rates of vertical ground motion in intraplate settings and to identify the various causes of these motions since 1999 we have carried out yearly campaigns of simultaneous gps measurements at 12 sites situated so as to sample the different tectonic subunits of the study area and especially to record potential displacements across the seismogenic hockai fault zone five campaigns 1999 2003 have been processed currently key issues of the data processing with the gamit software are discussed and first results are presented though temporally consistent in many cases the obtained vertical motion rates are spatially highly variable they are also much too high several mm year to support a tectonic interpretation and a long term influence of groundwater level variations is proposed to account for the observed motions this influence should be distinguished from seasonal variations and from inter survey variations linked to the varying degree of soil and subsoil drying off during the successive spring surveys

long lived crustal scale fluid flow the hydrothermal mega breccia of hidden valley mt painter inlier south australia the palaeozoic hidden valley breccia in the northern flinders ranges of south australia is exceptional for 1 its size of about 10 km2 2 the large continuous range in clast sizes from tens of microns to hundreds of metres and 3 thorough mixing of lithologies of different provenance some originally kilometres apart stratigraphically the size distribution follows a single fractal dimension of about unity over at least 6 orders of magnitude implying that a single process was responsible for diminution from the 100 m scale down to 12 km exhumation which lasted about 200 myrs starting during the 500 ma delamerian orogeny and continuing during the alice springs orogeny fluids released during exhumation were structurally focussed towards hidden valley where an estimated 20 5 30 km3 total fluid volume caused the extensive brecciation brecciation initiated in neoproterozoic cover metasedimentary rocks at a level that is now fully exhumed as hydrothermal fluid ascent continued with ongoing exhumation the level of brecciation shifted down into the underlying mesoproterozoic basement rocks taking with it clasts of cover rocks in this model rocks pass through the zone of brecciation which can thus incorporate a variety of lithologies that were originally kilometres apart

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits

an integrated gravity model for europe s crust and upper mantle we present an integrated gravity model of the european lithosphere based on an analysis of a number of new data sets leading to a much higher resolution than provided by previous models first of all a recent crustal model eucrust 07 is used to quantify the crustal contribution to the observed gravity field and to identify the effect of mantle heterogeneity the new gravity field model is based on a combination of satellite champ and grace and terrestrial data we also use these data sets to estimate residual mantle gravity anomalies and residual topography reflecting the effect of mantle density variations induced by temperature and compositional heterogeneity the separation of these effects is vital for a proper assessment of mantle structure and evolution in addition we utilize a new tomographic model for p and s velocity anomalies beneath europe which is a priori corrected for crustal structure using eucrust 07 the seismic velocity anomalies were subsequently converted into temperature anomalies using a mineral physics approach we estimate the effect of temperature variations on the gravity field and subtract it from the total mantle field the residual fields point to an important role of compositional density anomalies in the upper mantle a number of key features of the compositional density distribution so far invisible in seismic tomography data are detected for the first time

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

lithospheric response to volcanic loading in the southern cook islands abstract the response of the ocean lithosphere to volcanic island loading has been investigated for the southern cook islands of rarotonga mangaia and the aitutaki mauke group using 1 estimates of the change with distance from the load of uplift of islands located on the flexure created arch 2 geoid height perturbations as observed with the geos 3 and seasat radar altimeters and 3 bathymetric evidence for the moat and arch about the island loads the effective flexural rigidity for rarotonga is found to be higher than for the older and nearby islands of mangaia and aitutaki this together with an earlier result for tahiti 1 suggests that stress relaxation of the lithosphere has occurred and that this layer behaves as a viscoelastic material with an effective viscosity of about 5 10 10 25 poise the observations for the flexural rigidity do not indicate any dependence on the age of the lithosphere at the time the loading occurred this suggests that there are no significant differences in lithospheric properties for plates in the age range of 6 7 10 7 years altimeter passes to the east of mauke indicate that there may be an uncharted submarine extension of the aitutaki mauke chain

natural fracture propping and earthquake induced oil migration in fractured basement reservoirs the geological processes that create fluid storage capacity and connectivity in global fractured basement reservoirs are poorly understood compared to conventional hydrocarbon plays hosting potentially multibillion barrels of oil the upfaulted precambrian basement of the rona ridge offshore west of shetland uk gives key insights into how such reservoirs form oil presence is everywhere associated with sub millimeter to meterthickness mineralized fracture systems cutting both basement and local preseal cover sequences mineral textures and fluid inclusion geothermometry suggest a low temperature 90 220 c near surface hydrothermal system as does the preservation of clastic sediments in the same fractures these fills act as permanent props holding fractures open forming long term fissures in the basement that permit oil ingress and storage calcite fill u pb dating constrains the onset of mineralization and contemporaneous oil charge to the late cretaceous the additional preservation of oil stained injected sediment slurries and silica gels along basement faults suggests that rift related seismogenic faulting initiated lateral oil migration from jurassic source rocks into the adjacent upfaulted ridge subsidence below sea level in the latest cretaceous sealed the ridge with shales and buoyancy driven migration of oil into the preexisting propped fracture systems continued long after the cessation of rifting these new observations provide an explanation for the viability of sub unconformity fractured basement reservoirs worldwide and have wider implications for subsurface fluid migration processes generally

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

crystal growth diagrams as an aid to interpreting the fabrics of calcite aggregates abstract the morphological and optical properties of crystal aggregates which develop by nucleated growth from a plane substrate are modelled by crystal growth diagrams such diagrams show that fabric maturation occurs through three growth stages 1 isolated 2 competitive and 3 parallel diagrams are presented which are constructed using calcite rhombohedra of equant 1011 obtuse 0112 and acute 4041 form the acute form develops in the most mature parallel growth stage length fast columnar crystals this graphical model is matched by a natural calcite cemented neptunian dyke the obtuse form develops in the most mature parallel growth stage approximately length slow bladed crystals this graphical model is matched by a natural calcite cemented dilational vein diagrams are presented which show seeded in contrast to nucleated growth seeding produces overgrowths which are divisible into an early epitaxial stage of rapid growth and a later idiomorphic stage the volume of epitaxial growth depends on surface area shape and lattice perfection of the seed and on the crystal habit of the overgrowth the overriding importance of echinoderm skeletal elements in stimulating epitaxial growth in limestones is related to their large size relative to other seeds and to their lattice properties polycrystalline seeds with parallel c axis orientation develop overgrowth aggregates which omit the competitive stage because the crystals are constrained to develop normally to seed surfaces even when these are not the directions of most rapid growth growth from polycrystalline seeds with random c axis orientation produce crystal aggregates similar to those developed by nucleation from a passive substrate crystal growth diagrams are presented to show the effect of a change in crystal habit during continuous growth the acute to obtuse change examined results in the crystal s greatest growth vector s being reorientated which in turn causes a new episode of fabric maturation this graphical model is matched by a calcite cement from a south wales grainstone t shaped crystals growth hiatuses on some crystal surfaces and enfacial junctions are created in both model and natural example the use of crystal fabrics in the diagnosis of cement the correlation between crystal fabric and saturation state and the standard of crystallographic observation in studies of calcite cement are criticized the match between accurately drawn crystal growth diagrams and natural crystal aggregates is excellent these diagrams are an underused aid in the stereological assessment of crystal aggregates and reveal features that are not intuitively obvious

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

chaotic breccia along the dent fault nw england implosion or collapse of a fault void a body of chaotic breccia along the reverse oblique dent fault zone is ascribed to hanging wall collapse into persistent voids created by geometric mismatch of fault walls although some implosion into transient voids is a possibility the breccia comprises a 20 m wide body of hanging wall lithologies with a chaotic clast supported fabric that contrasts with the fitted fabric breccias typical of the dent fault damage zone the breccia body has crude bedding defined by clast shape and size contrasts the void fill is cut by variscan fault strands which together with its ferroan calcite and barite cement prove its late carboniferous rather than recent age it is shown that any fault void transient or persistent had a smaller aperture than the final width of the breccia body and no more than 5 m a span that can be supported to depths of 2 or 3 km however cement zonation in the breccia fill suggests that the void opened in multiple increments each of an aperture compatible with the maximum displacement in any one event along the dent fault the dent fault example highlights the possible general importance of fault void collapse but also the problems in distinguishing it from implosion processes

paleomagnetic dating of fracturing using breccia veins in durness group carbonates nw scotland abstract a paleomagnetic study of red fault related breccia veins in the cambro ordovician durness group in nw scotland was conducted to determine the time of brecciation the origin of the veins and the nature and timing of associated fluid related diagenetic alteration the veins contain brecciated fragments of the host durness group and strike either east west or north south clasts of breccia cemented by calcite suggest multiple brecciation events the host durness limestone is a gray dolomite and contains a devonian chemical remanent magnetization crm that resides in magnetite the veins contain magnetizations that reside in hematite and are interpreted as crms the breccias in north south veins contain a triassic crm whereas the veins with east west strikes contain a jurassic crm authigenic hematite is common in the breccias along growth planes in the calcite cements the two crms within the veins are interpreted as dating two separate brecciation and fluid flow events that precipitated authigenic hematite the brecciation and fluid flow events are interpreted to be related to extension in the mesozoic which is consistent with the extensional history of the northern atlantic margins

the post glacial landscape evolution of the north german basin morphology neotectonics and crustal deformation the recent evolution of the north german basin ngb which is presently a low seismic area was partly affected by glacial loading and unloading of the ice masses major stresses acting within the ngb are induced by the north atlantic ridge push the ongoing alpine collision and the post glacial rebound of fennoscandia present day horizontal stresses within the ngb are directed generally nw se but fan and bend north of 52 n towards nne major basement faults are directed nw se minor faults ne sw and nne ssw and are clearly detectable in geomorphological and satellite lineaments furthermore the drainage pattern and the distribution of lakes in northern germany follow exactly block boundaries and hence mark zones of present day subsidence the understanding of the post glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the ngb the re adjustment of the individual fault blocks during post glacial relaxation of the lithosphere leads to differential crust dependent uplift and probably to the formation of urstrom valleys the urstrom valleys and terminal moraines in northern germany appear to parallel the major tectonic lineaments and lithospheric block boundaries the lithospheric memory is expressed in the post glacial landscape evolution of the ngb

the viscosity of the mantle summary creep under low stresses is by diffusion and has a linear relation between stress and strain rate it also obeys the navier stokes equation therefore the viscosity of the mantle may be calculated from solid state theory and also from the slow deformations of the earth the viscosities derived by these methods are in reasonable agreement and both show that the viscosity of the lower mantle is lo5 greater than that of the upper this high viscosity prevents polar wandering and lower mantle convection some suggested modifications of the viscosity depth calculations from post glacial uplift may improve their accuracy considerably 1 the non hydrostatic equatorial bulge all calculations concerned with post glacial uplift haskell 1935 mcconnell 1965 and with convection within the mantle pekeris 1935 have used a linear relation between stress and strain rate creep in the material then obeys stokes equation and therefore may be described by a viscosity which is independent of stress such creep only takes place at stresses below the yield stress p where p is the shear modulus at higher stresses the relation between stress and strain rate is non linear see pratt above at stresses below the yield point diffusion creep alone can operate and it has a linear relation between stress and strain rate the diffusion creep rate also depends exponentially on temperature gordon 1965 and therefore is not sufficiently rapid to be measurable under ordinary laboratory conditions for this reason solids were believed to be unable to deform for stresses below the yield stress a concept called finite strength the stresses caused by the melting of ice caps by the non hydrostatic bulge and by regional temperature differences are probably less than the yield stress thus the viscosity will be stress independent and the equation of a maxwell solid should describe the flow however there are regions where earthquakes occur and where this argument is clearly false the viscosity of the mantle between the crust and a depth of ioookm may be found from the uplift of formerly glaciated areas mcconnell 1965 finds the uplift of fennoscandia can be explained if the viscosity is least at a depth of about 300 km increasing both upwards and downwards fig 2 the viscosity of the lower mantle which is of considerable importance to theories of convection and polar wandering unfortunately cannot be calculated from the uplift for two reasons the first is that the depth to which the flow penetrates in a homogeneous half space is about equal to the radius of the applied load or about 1000 km for fennoscandia this difficulty can be overcome when the uplift of the canadian shield has been measured if however mcconnell is correct and there is a viscosity minimum at a depth of about 300 km a second difficulty arises because the flow in the low viscosity layer will shield the lower mantle from the applied force it is therefore unlikely that any surface load can be used to estimate the viscosity of the lower mantle

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

large scale relief development related to quaternary tectonic uplift of a proterozoic paleozoic basement the armorican massif nw france the topography of basements located in intraplate domains has often been interpreted in terms of planation theory by examining the remnants of paleosurfaces in this paper we address the significance of the present day drainage networks that erode such topographies by looking at the relief development on the armorican massif basement northwestern france using digital elevation model dem analysis the topography of this massif is characterized by large scale 250 km relief variations that define high elevation domains heds these domains control the pattern of drainage networks by setting the location of the main drainage divides and the polarity of the regional slopes large scale relief is strongly associated with the existence of scarps along inherited fault zones suggesting that relief development is mainly controlled by tectonics through fault reactivation a surface evolution study shows that drainage networks developed during the quaternary which corresponds to the timing of the tectonic activity which also led to relief development the study of quaternary fluvial erosion through a new method for measuring incision shows that the drainage basins of the heds record greater amounts of base level fall during quaternary times this implies that differential uplift is responsible for the large scale relief development of the armorican massif during the quaternary our study suggests that as seen in active settings the topography of basements corresponds to a dynamic signal between tectonics and erosional processes which can be used for example in the study of intraplate deformation

lithospheric memory state of stress and rheology neotectonic controls on europe s intraplate continental topography abstract to date research on neotectonics and related continental topography development has mostly focused on active plate boundaries characterized by generally high deformation rates the intraplate sedimentary basins and rifts of the northern alpine foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that europe s intraplate lithosphere is being actively deformed this has major implications for the assessment of its natural hazards and environmental degradation the lithosphere of the northern alpine foreland has undergone a polyphase evolution with an intense interplay between upper mantle thermal perturbations and stress induced intraplate deformation that points to the importance of lithospheric folding of the thermally weakened lithosphere in this paper we address relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography the objectives are to quantify the effects of ongoing alpine collision and atlantic ridge push on the intraplate deformation in europe and its impact on topography evolution and related natural hazards this paper reviews the four dimensional topographic evolution of the european lithosphere through a multi disciplinary approach linking geology geophysics and geotechnology until now research on neotectonics and related topography development of intraplate regions has received little attention our study examines a number of selected natural laboratories in continental europe from orogen through platform to continental margin these natural laboratories include the carpathians pannonian system the northwest european platform iberia and the atlantic continental margin we focus on lithosphere memory and neotectonics with special attention to the thermo mechanical structure of the lithosphere mechanisms of large scale intraplate deformation late neogene anomalies in subsidence and uplift and links with surface processes and topography evolution

relationship between karstification and burial dolomitization in permian platform carbonates lower khuff oman large breccia fabrics associated with karst constitute an important structure in massive limestone successions the dimensions and shapes of breccia structures are controlled by the initial fracture pattern of the limestone and preferential pathways of the karstifying fluids but subsequently breccia fabrics can also govern the migration of later fluids therefore breccias are highly relevant features to capture for reservoir characterisation outcrop analogues for lower khuff units in the middle east present in the central oman mountains reveal brecciated fabrics up to 10 s of meters in diameter these brecciated units are closely associated with dolomite bodies of late diagenetic origin based on an integrated set of data the breccias are interpreted as collapsed karst cavities either formed by meteoric or hypogenic fluids the exact origin of the fluids could not be constrained due to an overprint by later dolomitizing fluids based on the composition of the clasts and matrix in the breccias two dolomitization events are interpreted to have affected the succession one prior to early diagenetic ed dolomite and one after brecciation late diagenetic dt2 dolomite dolomite of shallow burial origin ed dolomite was only observed as clasts within breccia and is much more frequent than late diagenetic medium to deep burial dolomite clasts thus the timing of the brecciation and collapse is assumed to postdate shallow burial early diagenetic dolomitization late diagenetic replacive dolomite dt2 dolomite forms 90 of the matrix in the breccia fabrics with the exception of a small area that was not affected by dolomitization but is rarely present as clasts stable isotope measurements 18o 2 5 to 6 vpdb and 13c 2 9 to 4 8 vpdb suggest a burial origin for the late diagenetic dolomite potentially with the participation of hydrothermal fluids the dolomitized matrix indicates a migration of late dolomitizing fluids subsequent to or postdating the collapse of the karstic cavities thus early karstification processes seem to have played a big role in controlling subsequent loci of late dolomitization in the oman mountains and potentially in other similar settings elsewhere