the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

the application of computer assisted photogrammetric methods in the structural analysis of part of the north greenland fold belt abstract the development of computer support in photogrammetric measurements has facilitated quick calculations of structural geological elements such as strike and dip fold axes and axial planes computer assisted photogrammetric methods have been applied in a structural analysis of 3000 km2 in central peary land north greenland detailed studies have been carried out in an area covered by a single stereo model representing part of the southernmost margin of the north greenland fold belt on the basis of the aerial photos a map with both lithological boundaries and structural measurements may be drawn in little known areas with complex structural relationships field work is necessary to control the interpretation in the present study refolded thrust fault structures were investigated preparatory photogrammetric studies allow the limited time available for field work to be effectively utilised and accurate geological maps to be produced relatively quickly

limitations on the role of pore pressure in gravity gliding a simple model has been developed to evaluate the gravity gliding of nappes in sedimentary terranes three factors play a critical role in the model 1 the ratio of horizontal to vertical stress 2 the rate of fluid flow to the detachment horizon and 3 the permeability of lithologies immediately above that horizon if the ratio of horizontal to vertical stress is less than one this ratio limits the maximum attainable pore pressure through hydrofracture existing in situ stress measurements suggest that vertical hydrofracturing rather than gravity gliding might be the result of elevated pore pressures unless a low strength cap rock exists if the stress ratio exceeds one a relatively simple equation relates the cap rock permeability and fluid flow necessary for gravity gliding effective cap rock permeabilities less than 10 sup 4 to 10 sup 5 md are required for gravity gliding in a sedimentary basin based on available in situ permeability measurements only shales and evaporites could have sufficiently low permeabilities on a regional scale 24 references

structure and organization of the porma melange progressive denudation of a submarine nappe toe by gravitational collapse the porma melange is a unit up to 1 km thick underlying the forcada nappe in the variscan foreland of the iberian peninsula most of the porma melange consists of a highly deformed boudinaged sequence with extension values over 300 percent the boudins or melange blocks are the result of bed parallel extension in two perpendicular directions giving rise to equidimensional boudins in plan view choco late tablet structure in cross section view the boudins show different shapes rectan gular rhomboid triangular trapezoid or with arrowhead edges due to various combinations of extension and shear fractures both the provenance of the melange blocks mostly derived from the upper part of the bodon nappe that overlies the forcada nappe and flattening type strain ellipsoid shapes support the interpretation that hanging wall gravitational collapse of these nappes was the cause of the exten sional deformation the current distribution of the melange blocks from different nappe formations implies progressive unroofing of the nappe stack through subse quent submarine slumps the internal structure of the melange blocks depends on the degree of sediment lithification during slumping and illustrates the significance of the so called native and exotic blocks the source of most of the melange material shaly matrix and native blocks or boudins was the semilithified syntectonic sediments of the upper part of the bodon nappe which underwent brittle ductile deformation boudinage during slumping however a few and usually larger exotic blocks also came into the basin as individual slip blocks from competent well lithified formations originally located at the lower part of the nappe stack with higher shear resistance and less suitable for spreading thus the arrangement of major nappe fragments traditionally named klippes and showing sizes that may reach up to several kilometers does not agree with the geometric rules of thrusting and are reinterpreted as megablocks resulting from gravitational sliding during denudation of advancing nappes

the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

sedimentary and structural evolution of a pleistocene small scale push moraine in eastern poland new insight into paleoenvironmental conditions at the margin of an advancing ice lobe abstract recent studies of push moraines have focused on the interplay between the dynamics of ice margins and the environmental variables of the foreland into which they advance these studies showed that the spatial distribution geometry and style of the glaciotectonic deformation of push moraines are controlled by ice induced stresses the strain rate the rheology of the deposits and hydraulic conductivity in this work we provide new insight into this interplay at a small spatio temporal scale specifically the ancient glacial system of the liwiec ice lobe within the younger saalian ice sheet in eastern poland the paleoenvironmental variables that are analysed here refer to the dynamics of the hydrological processes that affected the patterns and sediment deposition rate on the terminoglacial fan and the resulting mechanical stratigraphy and hydraulic conductivity of the foreland we document the progradational sequence of the fan deposits that developed as a result of the ice lobe thickening and the steepening of its stationary front the sedimentary features of the fan the lithology of its basement and the hydraulic conductivity of the foreland strongly influenced the geometry and kinematics of fold growth during the advance of the ice lobe the predominance of flexural slip and the development of fractures including fold accommodation faults were interpreted to be an effect of buckle folding due to horizontal shortening induced by ice advance the partial overriding of the push moraine by the ice lobe and thus the submarginal conditions for deformation were inferred from the significant hinge migration and internal deformation of the strata under undrained conditions in one of the folds the synfolding deposition pattern of the fan growth strata allowed us to suggest that the push moraine was probably formed by a sustained advance rather than surge

southwest scandinavia 40 15 kyr bp palaeogeography and environmental change twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the scandinavian ice sheet 40 15 kyr bp synchronised land sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon an interstadial sequence ca 40 30 kyr bp with boreo arctic proglacial fjords and subarctic flora and occasional glaciation in the baltic was succeeded by a last glacial maximum sequence ca 3020 kyr bp with the closure of fjords and subsequent ice streams in glacial lake basins in kattegat and the baltic steadily flowing ice from sweden bordered the norwegian channel ice stream a deglaciation sequence ca 20 15 kyr bp indicates the transgression of arctic waters retreat of the swedish ice and advance of baltic ice streams succeeded by a return to interstadial conditions when ameliorated ice free conditions prevailed in maritime regions glaciers advanced through the baltic and when interstadial regimes dominated the baltic glaciers expanded off the norwegian coast the largest glacier extent was reached in the north sea around 29 kyr bp about 22 kyr bp in denmark and ca 18 kyr bp in the baltic our model provides new data for future numerical and qualitative landform based models copyright c 2003 john wiley sons ltd less

seismic interpretation and structural restoration of the heligoland glaciotectonic thrust fault complex implications for multiple deformation during pre elsterian to warthian ice advances into the southern north sea basin abstract despite a long history of research the locations of former ice margins in the north sea basin are still uncertain in this study we present new palaeogeographic reconstructions of pre elsterian and warthian ice margins in the southeastern north sea basin which were previously unknown the reconstructions are based on the integration of palaeo ice flow data derived from glaciotectonic thrusts tunnel valleys and mega scale glacial lineations we focus on a huge glaciotectonic thrust complex located about 10 km north of heligoland and 50 km west of the north frisian coast of schleswig holstein northern germany multi channel high resolution 2d seismic reflection data show a thrust fault complex in the upper 300 ms twt ca 240 m of seismic data this thrust fault complex consists of mainly neogene delta sediments covers an area of 350 km2 and forms part of a large belt of glaciotectonic complexes that stretches from offshore denmark via northern germany to poland the deformation front of the heligoland glaciotectonic complex trends approximately nne ssw the total length of the glaciotectonic thrust complex is approximately 15 km the thrust faults share a common detachment surface located at a depth of 250 300 ms twt 200 240 m below sea level the detachment surface most probably formed at a pronounced rheological boundary between upper miocene fine grained pro delta deposits and coarser grained delta front deposits although we cannot rule out that deep permafrost in the glacier foreland played a role for the location of this detachment surface restored cross sections reveal the shortening of the complex along the detachment to have been on average 23 ranging from ca 16 50 the determined ice movement direction from east southeast to southeast suggests deformation by an ice advance from the baltic region the chronospatial relationship of the thrust fault complex and adjacent northwest southeast to northeast southwest trending elsterian tunnel valleys implies a pre elsterian mis 16 age of the glaciotectonic complex however the age of these elsterian tunnel valleys is poorly constrained and the glaciotectonic complex of heligoland may also have been formed during an early elsterian ice advance into the southeastern north sea basin the glaciotectonic complex underwent further shortening and the elsterian tunnel valley fills that were incised into the glaciotectonic complex were partly deformed during the saalian drenthe and warthe 1 ice advances

micromorphological evidence for the role of pressurised water in the formation of large scale thrust block moraines in melasveit western iceland pressurised meltwater has a major impact on ice dynamics as well as on sedimentary and deformational processes occurring below in front of glaciers and ice sheets but its role in glaciotectonic processes is yet to be fully understood this study explores micro and macroscale structures developed within decollements in two thrust block moraines of late weichselian age in melasveit western iceland the aim is to investigate how pressurised subglacial meltwater can aid the dislocation and transport of large unfrozen and unlithified sediment blocks by glaciers a detailed model is constructed for the development of the thrust block moraines and the microscale processes occurring along their detachments during thrusting the detachments are characterized by relatively thin zones of crosscutting hydrofractures which reflect fluctuating water pressures during glaciotectonism little evidence of shearing is observed along the leading edges of the thrusts in both moraines this is supported by high water pressures along the detachments and indicates that the thrust blocks were initially decoupled from the underlying deposits as the thrust moraines evolved an increased amount of shear occurred in between events of sediment liquefaction hydrofracturing and fluid escape this was followed by progressive locking up of the detachments and eventual cessation in the accretion of the thrust blocks

the engines of gravity driven movement on passive margins quantifying the relative contribution of spreading vs gravity sliding mechanisms movement of gravity driven systems on passive margins is fuelled by the loss of gravitational potential energy two end member modes gravity spreading and gravity gliding are defined by whether the potential energy loss is due to deformation and movement towards the base of the system spreading or by movement parallel to the base of the system gliding most natural systems consist of a mixture of the two processes hitherto use of these concepts has been limited or equivocal due to lack of a quantitative measure in some cases characterisation of gliding vs spreading systems based on secondary attributes has resulted in controversy because there is a lack of consensus as to which of these are truly diagnostic this paper presents a new simple quantitative method based on vector analysis providing a numerical measure of the relative contribution of spreading vs gliding the method is applied to synthetic examples where deformation can be tracked and to natural examples where a valid palinspastic reconstruction is available the results confirm that most natural examples exhibit mixed mode behaviour and that some have been mischaracterized much of the angola margin is dominated by spreading the method can also provide an estimate of the absolute amount of gravitational potential energy released in the movement and the energy contribution made by gliding vs spreading determining the dominant process has implications for predicting the development of seafloor topography and stratal architecture

gravity slide and resedimentation processes in a miocene carbonate ramp hyblean platcau southeastern sicily abstract more than twenty sharp based channel form structures occur in the miocene palazzolo formation carbonates within a distally steepened se sicilian miocene carbonate ramp contemporaneous biota indicate deposition in water depths of 70 150 m fully exposed structures commonly exceed one kilometre along palacostrike their bases are concordant with the host strata but these steepen to 15 in proximity of their margins internal bedding planes generally are concordant with the basal truncation surface the lithologies of the channel fills are similar to the host sediment there is little evidence that these structures are erosional since they contain neither breccias nor turbidites rather they are interpreted as the product of gravitational sliding involving thin detached sheets of consolidated ramp carbonates the resulting irregular topography was draped by redeposited fine grained carbonate sediments once healed and further oversteepened renewed gravity sliding occurred this resulted in a 250 m thick slide dominated succession in a zone 4 km wide located between the outer ramp apron comprised of coralline algal and foraminifera rich sediments and basin margin pelagic marls this phenomenon although unusual in shallow water settings is well known from modern continental slope environments sliding was probably triggered by seismicity in the region associated with two known mesozoic basement faults an alternative hypothesis involving pressure gradient build up along distally steepened ramp zones during storm surges is dismissed as a cause although this mechanism may have facilitated resedimentation of seafloor sediments over the slide zone

small scale faulting as an indicator of deformation mechanism in the tertiary sediments of the northern danish central trough abstract the tertiary sediments in the northern part of the danish central trough are characterized by a large number of small faults 25 50 m offset models for the accommodation of the deformation of the sediments are presented and it is shown quantitatively that a bending model best explains the observed strain distribution from this we infer that the internal deformation of the tertiary sediments is due to differential subsidence along older fault trends and not caused by applied external stresses on the tertiary sediments the effect of rock rheology and excess fluid pressure is discussed in order to explain the size of the throw and the smaller number of reverse faults compared to normal faults although the rocks are brittle they may in regions of shortening suffer more grainscale creep deformation than in regions of extension the strain distribution is determined on seismic sections and the main limitations of the method is thus the vertical and horizontal resolution of the seismic surveys used

the origins of glacially related soft sediment deformation structures in upper ordovician glaciogenic rocks implication for ice sheet dynamics in the upper ordovician glaciogenic rocks of west gondwana many soft sediment deformation structures are attributed to glaciotectonic processes however little is known about the subglacial and ice marginal processes associated with this ice sheet a systematic description and interpretation of these soft sediment deformation structures is supplemented by a comparison with late quaternary and modern glacial settings to provide qualitative constraints on the character of ancient subglacial thermal regimes soft sediment striations were formed by discontinuous shear induced deformation beneath an ice sheet that oscillated between warm and cold based thermal regimes beneath warm based ice coupling across the ice bed interface was poor with sliding and loading occurring at this surface loading of soft waterlogged sediments allowed the development of fluted surfaces which are also associated with the formation of truncated folded zones during times of cold thermal regimes coupling across the ice bed interface was enhanced by freezing which caused changes in the position of the freezing front these discontinuous changes coupled with sustained subglacial shearing resulted in the development of stacked soft sediment striated surfaces in areas where the subglacial substrate had an irregular topography complex shear zones formed that comprised stacked duplex systems interlayered with highly strained units preserving pervasive folded lineations at the ice front large glaciotectonic deformation structures comparable with push moraines developed during sustained periods of re advance that created composite thrust and fold systems deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance other deformation structures include dome like folds that consist of central anticlines 30 to 70 m in width with tight rim synclines that formed by the load induced diapiric intrusion of muds an ice sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs these surges potentially caused the widespread reorganisation of a glacial load resulting in the pro to subglacial extrusion of soft sediments

deep structure of the afro arabian hotspot by s receiver functions 1 we investigated deep structure of the afro arabian hotspot by using recordings from geoscope seismograph station atd the records are processed with the s receiver function technique which allows a detection of sp converted phases from the upper mantle discontinuities the seismic data reveal two unusual discontinuities the discontinuity at a depth of 160 km beneath the gulf of aden corresponds to the onset of melting if the water content in olivine is around 800 h 106si melting at this depth requires a temperature close to 1550 c about 120 c higher than the average another remarkable discontinuity is found at a depth of 480 km where s velocity drops with depth by about 0 2 km s this can be the head of another plume which is trapped in the mantle transition zone

structural architecture and glacitectonic evolution of the mud buttes cupola hill complex southern alberta canada this paper presents the results of a detailed multidisciplinary study of the deformed bedrock and overlying quaternary sediments exposed at the mud buttes in southern alberta canada this large arcuate cupola hill is composed of intensely folded and thrust sandstones siltstones and mudstones of the cretaceous belly river group glacitectonism responsible for the development of this internally complex landform occurred at the margin of the newly defined prospect valley lobe of the laurentide ice sheet analysis of the deformation structures reveals that construction of this landform occurred in response to at least two phases of south directed ice sheet advance separated by a period of retreat the first phase led to the formation of a forward propagating imbricate thrust stack leading to polyphase deformation of the belly river group d1 thrusting led to the detachment of thrust bound slices of bedrock which were accreted to the base of the developing imbricate stack this process resulted in the structurally higher and older thrust slices being progressively back rotated tilted accompanied by d2 thrusting and folding further thrusting during d3 was restricted to the core of the mud buttes as the deforming sequence accommodated further compression imposed by the advancing ice minor oscillations of the ice margin led to localised brittle ductile shearing d4 of the bedrock immediately adjacent to the ice contact part of the thrust stack the second phase of ice advance led to the accretion of a relatively simple thrust and folded sequence seen the northern side of mud buttes the resulting composite thrust moraine was subsequently overridden by ice advancing from the nnw to form a dome like cupola hill this readvance of the prospect valley lobe led to the formation of a thin carapace of quaternary sediments mantling the mud buttes which include glacitectonite till and an organic rich clay silt palaeosol

glacio tectonic structures a mesoscale model of thin skinned thrust sheets abstract a series of seven groups of push ridges ranging from 7 to 40 m in height 50 to 280 m in length and occupying a total width of more than 2 km mark the marginal zone of the a d 1890 maximum of eyjabakkajokull an outlet glacier of the vatnajokull ice cap iceland the internal structure of one ridge complex comprises two distinct elements a proglacial part which has been subject to compressional stresses resulting in the development of imbricate thrust sheets and a subglacial part which comprises low angle normal fault structures the two sub systems appear to be linked via a floor thrust and to have evolved together as the glacier reached the limit of its rapid advance in a d 1890

mechanisms of nappe emplacement at the southern margin of the damara orogen namibia abstract the naukluft nappe complex is exposed approximately 50 km south of the present southern margin of the late precambrian to early palaeozoic damara orogen this nappe complex overlies the autochthonous nama beds which belong to a platform area adjacent to the damara mobile belt the total displacement from the nw to the se amounts to 50 80 km the base of naukluft nappes is formed by a dolomite horizon ranging in thickness between zero and about 30 m recent investigations of the mineral content fluid inclusions grain fabric and deformation lead to the conclusion that continental playa lake evaporites must be assumed as source rocks of this dolomite this unit named the sole dolomite contains 35 different minerals with sparitic dolomite albite quartz tourmaline mg riebeckite talc and sericite being the main components the sole dolomite contains numerous rock fragments of granites granodiorites gneisses and mica schists with tourmaline and mg riebeckite as metasomatic minerals fragments of quartz albitolites which contain more than 50 vol of albite and various amounts of tourmaline and dolomite are very frequent the sole dolomite is extremely rich in fluid inclusions of different but mostly high salinity the minerals of the sole dolomite display no primary recrystallisation and no crystal plastic deformation no preferred lattice orientation is developed all deformation found in the sole dolomite is of the brittle type cataclastic mylonitisation without any preferred lattice orientation has been encountered only in the lowermost few centimetres of the sole dolomite in contrast to the sole dolomite the underlying autochthonous nama limestones have been transformed over a vertical distance of several metres into fine grained mylonites which reveal a well developed preferred lattice orientation the formation of these two types of mylonites will be discussed in more detail the sole dolomite is interpreted as a discordant intrusion under high pore fluid pressure into the base of a nappe sequence it may be assumed that before its lithification the water rich carbonate mush has acted as a lubricant the final displacement of the nappes with the sole dolomite at its base must have taken place after lithification of the intrusion otherwise the intense low temperature mylonitisation of the autochthonous and parautochthonous nama limestones cannot be explained adequately

probabilistic seismic hazard assessment for himalayan tibetan region from historical and instrumental earthquake catalogs the himalayan tibetan region has a long history of devastating earthquakes with wide spread casualties and socio economic damages here we conduct the probabilistic seismic hazard analysis by incorporating the incomplete historical earthquake records along with the instrumental earthquake catalogs for the himalayan tibetan region historical earthquake records back to more than 1000 years ago and an updated homogenized and declustered instrumental earthquake catalog since 1906 are utilized the essential seismicity parameters namely the mean seismicity rate the gutenberg richter b value and the maximum expected magnitude m max are estimated using the maximum likelihood algorithm assuming the incompleteness of the catalog to compute the hazard value three seismogenic source models smoothed gridded linear and areal sources and two sets of ground motion prediction equations are combined by means of a logic tree on accounting the epistemic uncertainties the peak ground acceleration pga and spectral acceleration sa at 0 2 and 1 0 s are predicted for 2 and 10 probabilities of exceedance over 50 years assuming bedrock condition the resulting pga and sa maps show a significant spatio temporal variation in the hazard values in general hazard value is found to be much higher than the previous studies for regions where great earthquakes have actually occurred the use of the historical and instrumental earthquake catalogs in combination of multiple seismogenic source models provides better seismic hazard constraints for the himalayan tibetan region

gravitational spreading of high terrain in ishtar terra venus magellan altimetry measurements indicate that the mountain belts and plateau margins of ishtar terra have topographic slopes in the range 2 30 magellan radar images reveal that numerous sets of narrow closely spaced troughs and lineations which we interpret as graben and normal faults are located in many of these regions of high slope the orientation of many of these graben sets perpendicular to the downslope direction suggests that they formed as a result of gravitational spreading in several of the mountain belts the extensional structures are parallel to the apparent direction of shortening consistent with the interpretation that gravitational spreading occurred while mountain building was still active to explore the implications of this spreading for the tectonic evolution of ishtar terra we model the process by means of a finite element algorithm for viscoelastic deformation in a vertical section of the crust at the margin of a plateau or broad mountain range flow in the crust is assumed to be governed by a nonlinear depth dependent rheology we predict brittle failure and relaxation of topographic relief as functions of time for ranges of crustal thickness 10 30 km and thermal gradient 5 25 k km and for observed ranges in topographic elevation 1 6 km and slope 1 30 this parameter range predicts a large spread in the time scales for initial failure and significant relaxation of relief for a crustal thickness greater than 10 km a thermal gradient of 15 k km or more and average values of relief 3 km and slope 3 the topography relaxes to 25 of its original height in less than 10 m y although initial failure in the form of normal faulting on the highlands and margin and occasional shallow thrusting in the lowlands is predicted to occur much earlier values of horizontal surface strain that are likely to be observable 1 do not accumulate until significant relaxation of relief begins given the predicted rate of topographic relaxation either the crust of ishtar terra must be anomalous in some way either much stronger than predicted by standard flow laws or very thin or cold or the topographic relief and high slopes have been actively built and maintained until times significantly younger than the average crater retention age for venus of 500 ma the large apparent depth of compensation the abundance of volcanism and the uncertainty in the local age favor the view that mountain building in ishtar terra has occurred until times at least as recent as 10 ma

sedimentary and tectonic architecture of a large push moraine a case study from hagafellsjokull eystri iceland original article can be found at http www sciencedirect com science journal 00370738 copyright elsevier b v full text of this article is not available in the uhra

mid pleistocene thin skinned glaciotectonic thrusting of the aberdeen ground formation central graben region central north sea this paper presents the results of a high resolution 2d seismic survey of mid pleistocene glaciogenic sediments in the central graben region of the central north sea sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid pleistocene ice sheet the total observed length of the thrust stacked section is approximately 5 6 km comprising a series of discrete thrust slices which range in length from 700 m the basal detachment of the thrust complex occurs at a depth of ca 220 m below the sea bed within the upper aberdeen ground formation a thin skinned glaciotectonic model involving proglacial to ice marginal glaciotectonic thrusting followed by post tectonic deposition is proposed initial ice advance led to the over pressurizing of groundwater within a laterally extensive sand sheet in the upper aberdeen ground formation promoting the formation of a major decollement surface at the base of the developing thrust stack over pressurization of the groundwater system is thought to have occurred in response to rapid ice advance suggesting that the development of large scale thrust complexes may be associated with surge type behaviour the proposed model evidences complex dynamics of mid pleistocene ice sheets within the central north sea

sedimentation in an ice contact subaqueous setting the mid pleistocene north sea drifts of norfolk u k in east anglia the mid pleistocene north sea drifts extend over some 1500 km2 of the coastal zone of north norfolk they are the oldest pleistocene glacial sequences exposed in britain deposited during the anglian glaciation ca 450 ka bp laminated and stratified pebbly mud diamict facies of the north sea drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin in this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body laminated stratified and massive diamict facies were deposited by the rain out of fine grained sediment from suspension and coarse debris from floating ice combined with downslope sediment gravity flow intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east away from a major ice marginal moraine ridge the cromer ridge exposures at cromer show bulldozed ice contact subaqueous sediments and ice thrust chalk rafts a fall in water level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan shaped sag basins with diapiric structures at their margins comparable sedimentary sequences are exposed elsewhere around the southern north sea basin a glaciomarine setting in response to glacio isostatic depression around the anglian ice sheet is suggested

numerical modelling of thrust structures in unconsolidated sediments implications for glaciotectonic deformation abstract the mechanics of thrust faulting induced by a differential vertical load has been studied by application of a dynamic finite element model the modelled scenario is analogous to the glaciostatic load imposed onto an unconsolidated sedimentary substrate by a stationary ice sheet the objective is to evaluate whether large scale glaciotectonic deformation may be induced by gravity spreading in front of a stationary glacier or if a push from the rear is required the model is capable of handling large strains and rotations combined with visco elastic plastic rheologies model parameters are derived from a pleistocene large scale glaciotectonic thrust complex in the eastern danish north sea the plastic behaviour of the unconsolidated sediments is described by a time and pressure dependent drucker prager yield criterion combined with a non associated flow law the modelling results show that gravity spreading in front of a stationary ice sheet can form strain localisations and possibly cause thrust faults to nucleate in unconsolidated sediments several kilometres beyond the snout of the ice sheet provided a decollement surface is situated at a suitable depth relative to the effective load of the ice sheet hence it is concluded that large scale glaciotectonic thrusting may be formed by gravity spreading alone and a push from the rear is not generally required to explain the observed deformation