a numerical model of deformation and fluid flow in an evolving thrust wedge abstract to investigate deformation and fluid flow in an actively deforming tectonic wedge we model the evolution of a large two dimensional 100 km long 5 km thick mechanically and hydrologically homogeneous and isotropic pile of sedimentary strata that is deformed to become a thrust wedge we compare both dry and wet cases in order to illustrate 1 the relative importance of fluids on wedge evolution and 2 the effect of brittle deformation on fluid flow we use an elastic plastic constitutive relation including a mohr coulomb failure criterion and a non associated flow rule and coupled fluid flow with bulk rock properties that approximate typical foreland sedimentary strata simulations are made both with and without dilation the model is fully dynamic but inertial forces remain small results show that deformation within the wedge is accommodated by reverse slip movement on shear bands which migrate in both directions through the wedge as both fore and back thrusts the model has features predicted by the critical taper theory 1 overall wedge geometry 2 crudely self similar growth during evolution 3 more intense deformation toward the rear of the wedge the models show strong overall in sequence faulting behavior with major thrusts isolating relatively undeformed packages which are moved in a piggyback manner upon the active thrusts intermittent out of sequence faulting does however occur in order to maintain the wedge taper fluid flow in the deforming wedge is dominated by topography but is also strongly affected by dilational plastic deformation in all simulations there is focused fluid flow within fault zones when mechanical time stepping is shut off uncoupled flow systems evolve to steady state where inflow equals outflow by subtracting the two states we isolate the mechanical fluid response from the total coupled system response the mechanical fluid response is manifest as contours of head and pressure difference and focusing of fluid flow in areas of active deformation in non dilational simulations these zones are quite localized and are a result of the contrasting stresses in and adjacent to a brittle shear zone in simulations with dilation the zones of head and pressure difference are broad and regional in extent they are ten times greater in magnitude than in non dilation simulations and they track a rock damage front that moves through the wedge

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

provenance of pliocene sediments and paleoenvironmental changes in the southern north sea region using samarium neodymium sm nd provenance ages and clay mineralogy abstract an 800 m thick sedimentary succession from the late pliocene north sea has been investigated on the provenance of the sediments and on changes of the source regions related to transport processes and climate changes the lower zanclean to piacenzian part of the succession from 1250 to 1050 m depth and the middle early gelasian part from 1100 to 700 m depth belong to one distributory system with at least two contributing source areas provenance ages calculated on basis of sm nd content indicate one old archean and one young

infill of tunnel valleys associated with landward flowing ice sheets the missing middle pleistocene record of the nw european rivers 1 the southern termination of the middle and late pleistocene scandinavian ice sheets was repeatedly located in the southern north sea sns and adjacent north sloping land areas giant meltwater excavated valleys tunnel valleys formed at the southern termination of the ice sheets and contain a hitherto enigmatic succession of northward prograding clinoforms comprising 1000s km3 of sediment this study analyses 3d seismic data covering the entire sns and demonstrates for the first time that the formation of these tunnel valleys was separate from their infill the infill constitutes the postglacial record of the nw european river deltas which had so far been considered missing

seven glacial cycles in the middle late pleistocene of northwest europe geomorphic evidence from buried tunnel valleys the deep ocean marine isotope record and the antarctic and greenland ice caps record numerous glacial and interglacial cycles since the middle pleistocene and yet evidence for similar numbers of ice sheet advances over the continent and shallow shelves of northwest europe is absent here we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the north sea basin between ca 500 and 40 ka consistent with that predicted by proxy records of glacial and interglacial climate change over 180 subglacial tunnel valleys that incise into pleistocene sediments in the north sea basin were mapped over 60 000 km 2 of three dimensional seismic reflection data using a subset of these data we identified seven separate episodes of subglacial erosion that can be correlated regionally in the uk sector of the central north sea the characteristics of the valley morphologies orientations and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice sheet advance and retreat cycle stratigraphic data suggest that the tunnel valleys formed significantly later than the brunhes matuyama reversal event at 780 ka and before the last glacial maximum marine isotope stage mis 2 21 ka these results imply a more complicated glacial history for northwest europe and more glaciations than the three glaciation model traditionally interpreted from the terrestrial record for the past 500 k y our data provide the most complete documentary evidence for repeated advance and retreat of the northwest european ice sheets since the middle pleistocene and for the first time indicate that terrestrial ice sheet advances in the north sea can be matched in number with the cold events recorded in oceanic and or ice core proxies of climate change over the past 500 k y

the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile journal of quaternary science 21 0 pp 1 15 sponsorship nerc rono ner b s 2002 00282

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

the pleistocene of schoningen germany a complex tunnel valley fill revealed from 3d subsurface modelling and shear wave seismics abstract the pleistocene deposits of schoningen represent an outstanding geological and archaeological archive where an up to 45 m thick middle to late pleistocene succession has been preserved and unique artefacts from the lower palaeolithic have been discovered the preservation of such a thick and complete glacial interglacial succession is very rare in the geological record and requires a specific depositional setting we will present a new depositional model for the pleistocene succession of schoningen integrating outcrop data borehole data and high resolution shear wave seismics a total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture all collected sedimentological and geophysical data sets were integrated into a high resolution 3d geological model gocad for reconstructing the spatial distribution of facies associations and the large scale depositional architecture the spatial distribution of the artefacts will be discussed with respect to the depositional environment the elsterian and holsteinian deposits are restricted to a nnw sse trending elongated trough which is deeply incised into unconsolidated lignite bearing palaeogene deposits the geometry of this erosional structure points to a tunnel valley origin that was incised below the elsterian ice sheet the basal tunnel valley fill consists of cross stratified pebbly sand and gravel overlain by till after deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition during the subsequent holsteinian interglacial mis 9 a lake formed within this depocentre and lacustrine sediments accumulated this interglacial succession consists of peat organic rich silt and fine grained sand interpreted as lake bottom and deltaic sediments fed by surface run off shed from the elm ridge the lacustrine deposition was controlled by repeated lake level fluctuations in the range of 1 6 m leading to the formation of laterally stacked delta systems these lake level changes were probably triggered by climate causing variations of precipitation and surface run off during the late saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits the sedimentary facies and depositional architecture point to a shallow water delta subsequently the meltwater deposits were overlain by till the deposition of the middle pleistocene sediments within an elsterian tunnel valley explains the unique preservation of the sedimentary succession of schoningen the long lived interglacial lake provided an attractive site for animals and early humans ambushing them artefacts mainly became embedded on the delta plain which rapidly was transgressed during lake level rise and artefacts were thus preserved

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

terrace styles and timing of terrace formation in the weser and leine valleys northern germany response of a fluvial system to climate change and glaciation abstract in glaciated continental basins accommodation space is not only controlled by tectonics and sea level but also by the position of ice sheets which may act as a regional base level for fluvial systems although the pleistocene terrace record of major river systems in northwestern europe has been investigated by many authors relatively little attention has been paid to base level changes related to glacier advance retreat cycles and how these regional changes in base level interacted with river catchment processes this study provides a synthesis of the stratigraphic architecture of middle pleistocene to holocene fluvial terraces in the upper weser and middle leine valley in northern germany and links it to glaciation climate and base level change the depositional architecture of the fluvial terrace deposits has been reconstructed from outcrops and high resolution shear wave seismic profiles the chronology is based on luminescence ages 230 th u ages 14 c ages and middle palaeolithic archaeological assemblages the drainage system of the study area developed during the early miocene during the pleistocene up to 170 m of fluvial incision took place a major change in terrace style from strath terraces to cut and fill terraces occurred during the early middle pleistocene before marine isotope stage mis 12 which may correlate with climate deterioration and the onset of glaciation in northern central europe during this time a stable buffer zone was established within which channels avulsed and cut and filled freely without leaving these vertical confines climate was the dominant driver for river incision and aggradation whereas the terrace style was controlled by base level changes during ice sheet growth and decay a major effect of glacio isostatic processes was the post elsterian re direction of the river weser and river leine the middle pleistocene fluvial terraces are vertically stacked indicating a high aggradation to degradation ratio corresponding with a regional base level rise during glacier advance at the beginning of the late pleistocene the terrace style changed from a vertical to a lateral stacking pattern which is attributed to a decrease in accommodation space during glacier retreat the formation of laterally attached terraces persisted into the holocene major incision phases took place during mis 5e 5d 5c and probably early mis 4 early mis 3 and mis 2 lateglacial during mis 5e and the lateglacial the braided river systems changed into meandering rivers indicated by preserved organic rich flood plain and point bar deposits the late pleistocene braided river systems mis 5c to mis 3 are characterized by a high sinuosity which may be a direct effect of an increased downstream gradient after deglaciation when the channel lengthened and the river adjusted to the increased gradient by increasing sinuosity these middle pleniglacial fluvial deposits are unconformably overlain by lateglacial to holocene meandering river deposits which form laterally attached terraces recording millennial scale channel shifts the lack of late pleniglacial deposits might be related to late weichselian forebulge formation

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

pt effects of pleistocene glacial periods on permafrost gas hydrate stability zones and reservoir of the mittelplate oil field northern germany abstract during the past two million years low surface temperatures as well as episodically advancing ice sheets from scandinavia acted on the subsurface pt regime of northern germany their likely effects on the petroleum system of schleswig holstein were investigated for the entire quaternary mean annual ground temperature magt was reconstructed at a resolution of 1000 years by calibrating oxygen isotope records from odp site 659 to the climate of northern germany of the past 120 kyr the resulting magt trend served as input to an ice sheet model and a permafrost model along a 2d section crossing the petroleum bearing south western part of schleswig holstein here advances and retreats of the scandinavian ice sheet during saalian and elsterian glaciation stages were reconstructed maximum ice thicknesses of up to 1700 m and up to 20 periods of regional permafrost in northern germany were reconstructed for the past 1 25 million years based on a basal heat flow of 50 mw m 2 permafrost thicknesses exceeded 100 m during most of these periods temporarily extending down to depths of more than 300 m favourable surface temperatures and long durations of cold periods provided favourable conditions for onshore gas hydrate stability zones at mittelplate implementing these glacial dynamics into 2d basin modelling petromod ies aachen germany of the mittelplate oil field reveals five phases of gas hydrate stability at depths down to 750 m the latest of these events occurred during the weichselian about 20 kyr ago the effect of the ice sheets on pore pressure in the subsurface strongly depends on the hydraulic boundary conditions at the ice base e g frozen vs temperate ice sheet base excess pore pressure in the reservoir of more than 10 mpa during ice overriding is possible and probable the calculated temperature effect of the pleistocene cooling on the mittelplate reservoir is in the range of 3 7 c even today temperature in the reservoir is still lowered by about 4 c in comparison to pre pleistocene times despite the fact that a significant influence of glacial effects on petroleum generation can be ruled out at mittelplate we state that pt effects in reservoirs related to glacial processes in formerly glaciated areas have been underestimated in the past

river incision and terrace formation in the late cenozoic of europe abstract late cenozoic environmental changes which affected european rivers are reviewed focusing especially on those of mid pleistocene times c 1 2 0 8 ma or around mis 22 and thereafter these involved dominating but fluctuating cold climate periglacial conditions shorter but major episodes of glaciation and brief interglacials there were also related sea level and tectonic responses the known history of european rivers in this period is individually varied but is predominantly marked by multiple stages of episodic incision the form of which changed in style at around the mid pleistocene transition it is suggested that the nature of climatic oscillations the dating of incision episodes and the processes that achieve this incision are as yet insufficiently understood fluvial process studies suggest that the onset of incision may broadly relate to changes in slope discharge sediment load and calibre and bedrock erodibility and these may all have been transformed as the direct or indirect result of mid pleistocene climatic changes common properties of basal sediments on strath terraces suggest that it was during the extended but variable cold stage episodes that both valley deepening and lateral widening occurred and that climatic change was the principal driver of episodic deep valley incision

an east west trending quaternary tunnel valley in the south eastern north sea and its seismic sedimentological interpretation a combination of a dense reflection seismic grid and up to 50 m long records from sediment cores and cone penetration tests was used to study the geometry and infill lithology of an e w trending buried tunnel valley in the south eastern north sea in relation to previously known primarily n s trending tunnel valleys in this area the geometry and infill of this 38 km long and up to 3 km wide valley is comparable but its e w orientation is exceptional the vertical cross section geometry may result from subglacial sediment erosion of advancing ice streams and secondary incision by large episodic meltwater discharges with high flow rates the infill is composed of meltwater sands and reworked till remnants on the valley flanks that are overlain by late elsterian rhythmic laminated lacustrine fine grained sediments towards the centre of the valley a depression in the valley centre is filled with sediments most likely from the holsteinian transgression and a subsequent post holsteinian lacustrine quiet water setting the exceptional axis orientation of this tunnel valley points to a regional n s oriented ice front during the late elsterian copyright 2012 john wiley sons ltd

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

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

evidence for a middle pleistocene glaciation of mis 8 age in the southern north sea abstract in the cores of borehole 89 2 situated at 54 00 01 n and 5 00 04 e about 70 km north of the frisian islands in the southern north sea two diamictons levels are found at 70 and 100 m below sea floor i e 110 and 140 below present sea level respectively both diamictons appear to be older than saalian mis 6 in contrast to earlier interpretations the upper diamicton is overlain by about 20 m of shallow marine sands followed by a chaotic alternation of fine grained clay rich eemian mis 5e sediments and sands deposited in a glacially excavated basin it was originally assumed that this diamicton was saalian mis 6 in age and lined the base of the basin seismic lines crossing the borehole location however show that the upper diamicton is truncated by the basin and consequently must be older than saalian this is corroborated by new investigations on the saalian eemian transition in the netherlands and new data on the age of the molluscs and foraminifera in the sands directly overlying the upper diamicton the age data based on measurements of the isoleucine epimerisation of mollusc shells and foraminiferal tests favour an mis 8 age

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

pre weichselian quaternary glaciations of the british isles the netherlands norway and adjacent marine areas south of 68 n implications for long term ice sheet development in northern europe within this paper we review the pre weichselian glacial history of northern europe focussing on evidence from the british isles netherlands norway and adjacent marine areas that record the activity of the british bis and scandinavian sis ice sheets the objective of the paper is to examine the long term evolution of the two ice sheets in order to determine their level of synchronicity and their relationship to the plio pleistocene record of northern hemisphere glaciation geological evidence demonstrates striking long term similarities between the behaviour of the bis and sis with a step wise intensification in the glacial signal 1 first ice rafted debris ird input onto the continental margin at ca 2 7 2 6 ma and restricted glaciation prior to ca 1 1 ma 2 initiation of more lowland style glaciation from 1 1 ma 3 repeated shelf edge glaciations from 0 45 ma these steps coincide with a major intensification of the northern hemisphere climate signal at the beginning of the quaternary and the mid pleistocene transition temporal and spatial variabilities in the behaviour of different sectors of the bis and sis appear to reflect regional scale geographic latitude elevation climatic moisture temperature and glaciological deformable beds controls that modulate the build up of ice volume in the main ice accumulation areas relative to global climate forcing and its subsequent lateral expansion 2010 nerc

high resolution seismic profile through a late cenozoic delta complex in the southern north sea abstract a digitally recorded and processed multichannel seismic profile between cromer england and sylt germany has provided the first continuous section through the miocene to middle pleistocene delta complex of the southern north sea basin the profile depicts the progressive westward expansion of deltaic sedimentation that eventually filled in this gently subsiding epicontinental basin significant basinward shifts in seismic facies occur above all but one of 14 seismic sequence boundaries that punctuate the deposition of up to 830 m of deltaic sediments on the profile these sequence boundaries and the morphology of prodelta delta front delta top and fluvio deltaic seismic facies record the interaction between subsidence cyclic fluctuation in sediment supply to and cyclic change of relative sea level within the basin two submarine slides were developed within delta front facies in the pliocene section and the profile has intersected a swarm of elsterian middle pleistocene glacial palaeovalleys that have been incised into the upper part of the delta complex

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

time transgressive tunnel valley infill revealed by a three dimensional sedimentary model hamburg north west germany deep elongated incisions often referred to as tunnel valleys are among the most characteristic landforms of formerly glaciated terrains it is commonly thought that tunnel valleys were formed by meltwater flowing underneath large ice sheets the sedimentary infill of these features is often highly intricate and therefore difficult to predict this study intends to improve the comprehension of the sedimentology and to establish a conceptual model of tunnel valley infill which can be used as a predictive tool to this end the densely sampled pleistocene tunnel valleys in hamburg north west germany were investigated using a dataset of 1057 deep wells containing lithological and geophysical data the stratigraphic correlations and the resulting three dimensional lithological model were used to assess the spatial lithological distributions and sedimentary architecture the sedimentary succession filling the hamburg area tunnel valleys can be subdivided into three distinct units which are distinguished by their inferred depositional proximity to the ice margin the overall trend of the succession shows a progressive decrease in transport energy and glacial influence through time the rate of glacial recession appears to have been an important control on the sedimentary architecture of the tunnel valley fill during periods of stagnation thick ice proximal deposits accumulated at the ice margin while during rapid recession only a thin veneer of such coarse grained sediments was deposited ice distal and non glaciogenic deposits i e lacustrine marine and terrestrial fill the remaining part of the incision the infill architecture suggests formation and subsequent infill of the tunnel valleys at the outer margin of the elsterian ice sheet during its punctuated northwards recession the proposed model shows how the history of ice sheet recession determines the position of coarse grained depocentres while the post glacial history controls the deposition of fines through a progressive infill of remnant depressions

geometry and kinematics of glaciotectonic deformation superimposed on the cenozoic fault tectonic framework in the central polish lowlands abstract the distribution of glaciotectonic structures can be controlled by the occurrence of tectonic or neotectonic faulting of the pre quaternary basement the faulted and thus undulated pre quaternary basement influenced the thinning or pinching out of weak deformable surficial sediments and could play a role of buried obstacles to forcing by ice sheets in both cases such faulting could result in a predisposition to the development of glaciotectonic deformations the present study has demonstrated how the geometry and kinematics of the glaciotectonic structures was controlled by the pre quaternary framework related to the kleczew graben tectonics the central polish lowlands the assumption has been made in this study that the tectonic fractures and faults could influence the reduction of strength and mechanical anisotropy within the pre quaternary sediments which were also remobilised by glaciotectonic forces the renewed stress build up by the glaciotectonic forces assumed herein could reactivate the pre existing fractures and faults at a lower stress level rather than produce new structures that require a higher stress level the results presented in this study are focused on detailed structural and kinematic analysis of the glaciotectonic faults and fractures for each glaciotectonic fault studied the slip vector was directly calculated based on the orientation of the fault striations and indirectly calculated from analysis of the small fractures that developed along the fault additionally the data from this analysis were integrated with the surface based 3d structural model obtained from the borehole data this approach revealed the relationships between the geometry orientation and kinematics of the glaciotectonic structures and the tectonic framework of the pre quaternary basement the different modes of glaciotectonic faulting were determined depending on the geometry and orientation of the pre existing reactivated faults and fractures with respect to the direction of the glaciotectonic contraction in addition to reverse dip slip displacements the strike slip and oblique slip displacements were recognised this study was performed in the kleczew graben the middle part of the polish lowlands in which the quaternary and the miocene sediments are affected by glaciotectonic deformations moreover the miocene sediments were also tectonically deformed in response to the development of the graben

3d seismic analysis of buried tunnel valleys in the central north sea morphology cross cutting generations and glacial history abstract this work presents the results of morpho stratigraphic analyses carried out on more than 180 buried tunnel valleys imaged in the central north sea using 3d seismic data at a variety of resolutions the buried tunnel valleys form complex networks of multiple cross cutting generations in the northern part of the study area cross cutting relationships within higher resolution 3d seismic data are used to extrapolate seven generations of tunnel valleys over an area of 14 400 km 2 three generations of cross cutting tunnel valleys are also observed within higher resolution 3d seismic data in the southern part of the study area detailed morphological measurements of individual tunnel valleys reveal average widths between 300 m and 3000 m lengths in the region of tens of kilometres and relatively straight and simple planform geometries the majority of the tunnel valleys display undulating basal profiles which provide evidence for the uphill movement of water over distances greater than 10 km and indicate formation by meltwater under pressure tunnel valley geometries vary between generations and defy a simple link between formation process and end form detailed orientation measurements for the tunnel valley generations reveal an overall ne sw trend in the northern part of the study area and a nw se directionality in the south when considered in light of palaeoglaciological models for the british and scandinavian ice sheets during the pleistocene tunnel valley orientation and distribution are consistent with the majority of tunnel valley generations forming perpendicular to a retreating british ice sheet changes in orientations between generations in both northern and southern study areas provide evidence for changes in the dynamics of the british and scandinavian ice sheets between subsequent glaciations of the central north sea

crustal structure in and around the onikobe geothermal area northeastern honshu japan inferred from the spatial variation of coda decay abstract the onikobe area is an active geothermal area situated in the ou backbone range of northeastern honshu japan it is home to calderas from the tertiary to quaternary eras and active volcanoes a systematic spatial variation of q c has been found in this area q c values are lower at stations in and around calderas than at other stations the amplitude of coda waves with high q c s decreases more slowly after a lapse time of around 7 10 s than that with low q c s in the present study to determine causes for these coda decay variations coda envelopes were synthesized in a structure model in which high attenuation zones existed beneath the onikobe and sanzugawa calderas and where scattering coefficients were higher in the lower crust than in the upper crust using hypocenters shallower than 10 km envelopes were calculated for 256 station hypocenter pairs with epicentral distances of less than 10 km it was assumed that the coda waves were composed of s s scattered waves and that the scattering was single and isotropic the observed features of the q c distribution were reproduced in the synthesis and synthesized envelopes were found to mostly coincide with observed decay curves the top of high attenuation zones was thus estimated as being deeper than 7 5 km the structure assumed for the synthesis was consistent with that of previous studies we consider that the structure model used was appropriate and that high attenuation zones beneath calderas and the reflective lower crust caused the spatial variation of the q c and decay curves in the onikobe area we also consider that studies using coda decay would be beneficial in detecting high attenuation zones and the reflective lower crust

aminostratigraphy of european marine interglacial deposits molluscan fossils collected from shallow water marine sediment across nw europe and nearby arctic regions have been analysed for the extent of isoleucine epimerization dl ratio in indigenous protein residues the dl ratios confirm that essentially all classical eemian sites from nw europe are of the same age and are correlative with the type locality near amersfoort in the netherlands shells from interglacial marine sediment beneath the type weichselian till in poland also correlate with the type eemian site dl ratios in holsteinian marine shells 0 29 are substantially higher than in their eemian counterparts 0 17 late cromerian shells yield even higher ratios 0 46 dl ratios in late glacial shells 0 06 and middle weichselian shells 0 09 permit differentiation from modern 0 01 and last interglacial material based on the position of the matuyama brunhes boundary and the differences in dl ratios the eemian must correlate with isotope substage 5e whereas the holsteinian is most likely substage 7c possibly stage 9 but certainly younger than stage 11 intra saalian warm periods may be terrestrial equivalents of the younger substages of stage 7 extensive pre eemian marine sediments along the sw coast of denmark previously correlated with the holsteinian are shown to be of late cromerian age the underlying till there is the first widespread evidence of a pre elsterian till in nw europe dl ratios in molluscs from last interglacial sites along the arctic coast of the ussr the arctic islands and eastern greenland are substantially lower than in their european counterparts due to their low thermal histories the combined mid and high latitude data are used to develop a predictive model for the expected dl ratio in any of several moderate epimerization rate taxa for last interglacial sites with mean temperatures between 20 and 15 c not all sites could be unambiguously assigned to an established interglacial the fjosanger norway and margareteberg sweden sites previously thought to be eemian yield dl ratios higher than in secure nearby eemian material it is yet unresolved whether these are aberrant sites or if they predate the last interglacial in situ shoreline deposits encountered in borings in sw belgium and in exposures on the belgium coastal plain contain molluscs that yield dl ratios intermediate between secure eemian and late weichselian ratios raising the possibility that a late stage 5 high sea level event attained near modern levels in the southern north sea basin resolution of these uncertainties is the focus of future work

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

response of salt structures to ice sheet loading implications for ice marginal and subglacial processes abstract during the past decades the effect of glacioisostatic adjustment has received much attention however the response of salt structures to ice sheet loading and unloading is poorly understood our study aims to test conceptual models of the interaction between ice sheet loading and salt structures by finite element modelling the results are discussed with regard to their implications for ice marginal and subglacial processes our models consist of 2d plane strain cross sections which represent simplified geological cross sections from the central european basin system the model layers represent i sedimentary rocks of elastoplastic rheology ii a viscoelastic diapir and layer of salt and iii an elastoplastic basement on top of the model a temporarily variable pressure simulates the advance and retreat of an ice sheet the durations of the individual loading phases were defined to resemble the durations of the pleistocene ice advances in northern central europe the geometry and rheology of the model layers and the magnitude spatial distribution and timing of ice sheet loading were systematically varied to detect the controlling factors all simulations indicate that salt structures respond to ice sheet loading an ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir resulting in an uplift of up to 4 m the diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir when the diapir is transgressed by the ice sheet the diapir is pushed down up to 36 m as long as load is applied to the crest of the diapir during and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow plastic deformation of the overburden is restricted to the area immediately above the salt diapir the displacements after unloading range between 3 1 and 2 7 m larger displacements are observed in models with deep rooted diapirs thicker ice sheets longer duration of the loading phase thicker salt source layers and lower viscosity of the salt the rise or fall of diapirs triggered or amplified by ice sheet loading are likely to affect glacigenic deformation erosion and deposition above the diapir and within the rim synclines ice load induced uplift in front of an ice sheet will provide favourable conditions for the formation of push moraines for example by creating a topographic obstacle and inclining potential detachments subglacial subsidence of salt structures will enhance erosion by providing a preferential drainage pathway and fracturing of the overburden of the salt structure and thereby contribute to the incision of tunnel valleys however the resulting displacements are probably too low to have a marked effect on the advance or retreat pattern of the ice sheets

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

reflections on soft subglacial beds as a mosaic of deforming and stable spots abstract much discussion regarding subglacial processes is centred around the question of how soft beds respond to ice overriding in particular how widespread and penetrative is their deformation how does it affect the ice stability and what are the consequences for large scale sediment redistribution patterns contrasting views have been proposed which are difficult to verify and reconcile in the light of scarcity of agreed criteria to identify deforming beds here we suggest that soft beds under warm based glaciers can be envisaged as a mosaic of deforming and stable spots transient in time and space according to changes in the control parameters at the ice bed interface the subglacial mosaic model is consistent with field data showing heavily deformed beds interspersed with largely undisturbed beds it is suggested that deformation found in tills is a cumulative effect of strain within a relatively thin ephemeral deforming spots under the ice sole affecting the till as it accretes during ice overriding in accord with the coulomb plastic rheology the role of clast ploughing in bed deformation is emphasised

neogene inversion of the central graben and ringkobing fyn high denmark abstract inversion in the north sea area and onshore denmark is a well known phenomenon and the main phase is interpreted to have occurred in the cretaceous and early cenozoic this study demonstrates an important early neogene inversion phase that resulted in the most distinct flexuring of the southern danish central graben during the cenozoic reactivation of structures on the ringkobing fyn high also took place during this inversion phase apatite fission track data confirm marked uplift of the marginal areas of the fennoscandian shield the recognition of the inversion of the ringkobing fyn high is based on new high resolution seismic data and has not been reported previously minor inversion pulses continued throughout the early and middle miocene and ceased in the early late miocene the early neogene inversion was the last major influence of the alpine orogeny in the danish area as a consequence of the early neogene inversion clastic sediments were flushed into the norwegian danish basin due to increased relief in the hinterland the high sediment supply continued throughout the early miocene despite changing climatic conditions from an overall cold temperate climate to a subtropical climate at the transition from the early miocene to the middle miocene the high sediment yield however ceased due to marked subsidence in the middle late miocene following the last inversion pulse in the middle miocene

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

glaciotectonized quaternary sediments at dinas dinlle gwynedd north wales and their bearing on the style of deglaciation in the eastern irish sea abstract the sedimentology and structure of late quaternary sediments exposed in a coastal section at dinas dinlle north wales are described the deposits from two small hills the northern one being more prominent and containing northward dipping units of gravel and diamicton bounded by clay lined thrust faults the southern hill comprises complex folded sands and gravels overlying a basal till surface high resolution seismic surveys along the beach 50 m west of the cliffs show a roughly horizontal rockhead lying some 35 m below beach level and demonstrate that thrust faults penetrate the entire quaternary sequence to a detachment immediately above rockhead thrust units in the exposed cliff section show excellent correlation with the seismic sequence 50 m to the west indicating a strike of 080 260 balanced cross section techniques were applied to an initial simple layered sequence comprising a lower irish sea till overlain by a coarsening upwards sand to gravel unit followed by upper till mixed lithology including welsh and northern provenance and finally an upper gravel unit shortening of approximately 54 is estimated within the thrust sequence it is concluded that the two isolated hills at dinas dinlle are erosional remnants of a formerly more extensive push moraine extending westwards into caernarfon bay which has now been truncated by coastal retreat deglaciation of the area was interrupted by ice sheet readvance towards 170 across a proglacial surface

ice thrust terrains and glaciotectonic settings in central alberta airphoto analyses geologic field mapping and study of borehole logs and surficial topographic maps in ice thrust terrains in central alberta suggest that all these techniques are needed to identify ice thrust terrains that may or may not have topographic expressions three geomorphological settings susceptible to glaciotectonic deformation are described as escarpment valley and plains settings the bedrock slopes in the escarpment setting ranged from 19 to 51 m km the bedrock slopes in the valley setting ranged from 23 to 32 m km and the valley was 8 5 km wide between crests and 4 km at the bottom the bedrock slopes of the plains setting ranged from 2 to 5 m km ice thrust features are found in topographic troughs in front of an ice sheet where water bodies were impounded these proglacial water bodies thawed the permafrost in front of the glacier the disintegration of proglacial permafrost decreased the resistance of subglacial strata to ice thrusting ice thrust features can be expected in areas wh

probability of moraine survival in a succession of glacial advances emplacement of glacial moraines normally results in obliteration of any older moraines deposited by less extensive glacial advances a process we call obliterative overlap a probability analysis of the likely impact of obliterative overlap on the completeness of the glacial record assumes that moraines were deposited at various distances from their glacial source areas randomly over time assuming randomness and obliterative overlap after 10 glacial episodes the most likely number of surviving moraines is only three the record of the pleistocene is in agreement with the probability analysis the 10 glaciations during the past 0 9 m y inferred from the deep sea record resulted in moraine sequences in which only two or three different aged moraine belts can generally be distinguished

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

deeply rooted glaciotectonism in western denmark geological composition structural characteristics and the origin of varde hill island we investigate a hill island in western denmark a major cupola hill type thrust complex generated by ice marginal glaciotectonism the study uses a unique dataset of densely spaced airborne electromagnetic data high resolution seismic data and borehole information to document the complexity of deeply rooted thrust sheets comprising miocene to middle pleistocene deposits the deformation spans at least 150 m of sediment thickness placing this complex among the largest glaciotectonic features on record the main stages of formation of the hill island were 1 erosion of miocene deposits by subglacial tunnel valleys and infill of these valleys in the pre elsterian and elsterian time 2 two phases of glaciotectonic thrusting during the saalian glaciation 3 erosion by the saalian ice sheet removing a significant part of the thrust complex and 4 periglacial and postglacial erosion of the hill island excavating the glaciotectonic elements palaeoglaciological calculations suggest that the saalian ice sheet that caused the thrusting was thick had a steep profile rested on a permafrost wedge and moved slowly which contrasts with the highly mobile thin ice lobes of the last glaciation

polyphase deformation at an oscillating ice margin following the loch lomond readvance central scotland uk the sequence of glacitectonic disturbance of an ice contact delta during the initial stages of deglaciation following the loch lomond readvance is examined an ice marginal gilbert type deltaic sequence exposed in drumbeg quarry drymen scotland displays a polyphase deformation history that is punctuated by periods of erosion and deposition progradation of the delta into ice dammed lake blane led to a temporary stabilisation of the loch lomond glacier during recession from its loch lomond readvance maximum position this was followed by a ne directed readvance into the ice contact slope of the delta resulting in proglacial deformation d1 and the formation of a thrust block ridge in the middle to outer parts of the delta complex sedimentation continued uninterrupted subsequent retreat of the ice was accompanied by erosion and deposition as the ice contact slope was re established a second phase of readvance resulted in subglacial ductile shearing d2 and deposition of a diamicton during ne directed over riding of the delta sediments by the ice the direction of ice flow subsequently changed towards the se this was followed by a further retreat of the ice and re establishment of the fan delta complex the complexity of the glacitectonic sequence at drumbeg records the impact of an oscillating ice margin responding to either relative deepening of the lake waters in contact with the receding snout or climatic controls it provides further evidence that many of the scottish highland glaciers were subject to active recession rather than stagnation at the end of the loch lomond readvance

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

flow mechanism of glaciers on soft beds subhourly measurements of bed deformation bed shear strength subglacial water pressure and surface speed at storglaciaren a glacier in northern sweden showed that the shear strain rates of the bed decrease during periods of high water pressure and surface speed high water pressures appear to be accompanied by a reduction in the coupling of ice with the bed that is sufficient to reduce or eliminate shearing the instability of large ice masses may result from similar decoupling rather than from pervasive bed deformation as has been commonly thought

geological history and petroleum system of the mittelplate oil field northern germany the geological history of germany s largest and most productive petroleum accumulation the mittelplate oil field in schleswig holstein northern germany is reconstructed by simulating the structural and thermal evolution along a 2d cross section the mittelplate field is located at the western flank of the busum salt dome at the transition from the schleswig holstein mainland to the german north sea sector organic geochemical data confirm the lower jurassic posidonia shale to be the predominant oil source rock in the schleswig holstein area the studied section is characterized by salt walls and salt domes built up by permian evaporites reconstruction of the structural and thermal evolution of the mittelplate field by means of basin modelling reveals the dominating influence of salt dynamics on the entire petroleum system the development of secondary rim synclines during salt rise provided accommodation space for the deposition of the posidonia shale as well as the deltaic middle jurassic reservoir sandstones the rise of the nearby oldenswort salt wall controlled the timing of maturation and petroleum generation during cenozoic times hydrocarbon migration from the posidonia shale into the reservoirs occurred up dip from the deeper subsiding rim syncline into the structural trap with the middle jurassic reservoir sandstones pinching out at the flank of the busum salt dome along the modelled 2d section the field s recent temperature field and its complex reservoir architecture are reconstructed