a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

high resolution landform assemblage along a buried glacio erosive surface in the sw barents sea revealed by p cable 3d seismic data abstract the quaternary sedimentary record in the arctic captures a diverse and evolving range of landscapes reflecting climate changes here we study the geological landform assemblage of the upper regional unconformity uru in the sw barents sea the aims are i to characterize buried geological landforms on a meter scale resolution ii to understand their link with underlying structures and iii to reconstruct paleo ice sheet dynamics and configurations the data consist of a high resolution three dimensional 3d p cable seismic cube with an extent of c 200 km2 and an inline separation of 6 m dominant frequencies of c 150 hz allow to image landforms at uru with a vertical resolution of 1 5 m and a horizontal resolution of 3 6 m we conduct detailed horizon picking and seismic attribute analysis of the buried uru horizon we identified four sets of mega scale glacial lineations and shear band ridges located to the west of a shear margin moraine other characteristic features include hill hole pairs transverse ridges rhombohedral ridges and depressions iceberg ploughmarks and pockmarks polygonal faults below uru and deeper faults have a strong effect on the location of structures observed on uru bedrock packages deformed down to 30 m below uru and up to 5 m high transverse ridges at uru are imprints of glacio tectonic activity deformed strata below uru indicate normal faulting superimposed by glaciotectonic deformation the four sets of mega scale glacial lineations indicate four streaming events with thawed glacial beds with shear band ridges forming in the shearing zone during one of these streaming events hill hole pairs and rhombohedral ridges are frozen bed features which indicate a polythermal regime at the base of the barents sea ice sheet during multiple streaming phases this study therefore shows that paleo ice streams have been temporarily frozen to the ground in the sw barents sea and that landforms evidencing this freezing are associated with underlying faults

cross hole fracture connectivity assessed using hydraulic responses during liner installations in crystalline bedrock boreholes abstract in order to continually improve the current understanding of flow and transport in crystalline bedrock environments developing and improving fracture system characterization techniques is an important area of study the presented research examines the installation of flexible impermeable flute liners as a means for assessing cross hole fracture connectivity flute liners are used to generate a new style of hydraulic pulse with pressure response monitored in a nearby network of open boreholes drilled in gneissic rock of the canadian shield in eastern ontario canada borehole liners were installed in six existing 10 15 cm diameter boreholes located 10 35 m apart and drilled to depths ranging between 25 45 m liner installation tests were completed consecutively with the number of observation wells available for each test ranging between one and six the collected pressure response data have been analyzed to identify significant groundwater flow paths between source and observation boreholes as well as to estimate inter well transmissivity and storativity using a conventional type curve analysis while the applied solution relies on a number of general assumptions it has been found that reasonable comparison can be made to previously completed pulse interference and pumping tests results of this research indicate areas where method refinement is necessary but nonetheless highlight the potential for use in crystalline bedrock environments this method may provide value to future site characterization efforts given that it is complementary to and can be used in conjunction with other currently employed borehole liner applications such as the removal of cross connection at contaminated sites and the assessment of discrete fracture distributions when boreholes are sealed recreating natural hydraulic gradient conditions

environmental significance of bedrock jointing in southern ontario canada the bedrock surface of many glaciated areas is obscured by thick drift deposits in southern ontario canada the buried bedrock surface is dissected by channels infilled with glacial deposits as much as 150 m thick that are part of a wider mid continent preglacial fluvial system that predates formation of the modern great lake basins the infills of bedrock channels form major groundwater aquifers influence regional groundwater flows and contaminant migration to lake ontario and may localize the release of thermogenic methane and radon within heavily urbanized surface environments a quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident buried bedrock channels in south central ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying pleistocene sediments joints in sediments are of considerable environmental significance for example subsurface contaminant and gas migration in fine grained clayey sediments and of many origins stress release desiccation etc but are widely assumed to be a predominantly surface related phenomena the existence of deeper joints has been noted by some authors but their origin is obscure data presented herein from south central ontario confirm that in addition to surface related joints a second population of bedrock related joints reflecting the upward propagation of bedrock fractures is present in pleistocene sediments of south central ontario

relationship between mega scale glacial lineations and iceberg ploughmarks on the bjornoyrenna palaeo ice stream bed barents sea abstract mega scale glacial lineations msgls are ridge groove corrugations aligned in the direction of the former ice flow tens of kilometers long and up to a few hundred meters wide they are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology despite the importance of msgls their formation remains enigmatic most studies have tended to focus on assemblages of msgls and their relationship to other landforms up ice e g drumlins or bedrock features in ice stream onset zones but fewer studies have examined their characteristics and transition to other landforms towards ice stream grounding lines in this paper we investigate the relationship between an assemblage of msgls and ploughmarks on the bed of the former bjornoyrenna ice stream in the sw barents sea which occurs in the central part of the ice stream bed a sample of msgls is used to test their potential origin based on their metrics width length and diagnostic characteristics predicted by formation theories results show a down flow depth decrease of the msgl grooves and a shallowing tendency once they transition into ploughmarks their width shows an increasing tendency which we link mostly to the strong divergence of the trough and ice flow downstream the prominent continuity from linear to curvilinear features demonstrates that the grooves associated with msgls transition into iceberg ploughmarks this observation is consistent with the hypothesis that the msgls have formed through a mechanism of groove ploughing at least in part the continuity from msgls to iceberg ploughmarks resulted from detachment of large icebergs from the grounded ice wall or grounded ice shelf and their ploughing away from the ice margin

the development of polygonal fault systems by syneresis of colloidal sediments abstract polygonal fault systems occur in numerous sedimentary basins worldwide are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting these fault systems have been most thoroughly described in the central north sea basin and the detailed structure shows a significant correlation with lithological variations both vertically and laterally extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content lateral facies variations are also observed and indicate that time equivalent sequences upslope from the smectite rich polygonally faulted sediments are coarse grained clay poor and undeformed this leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid this process occurs due to the domination of interparticle attractive forces in marine clays dependent on environment and is governed by the change of gel permeability and viscosity with progressive compaction the process of syneresis can account for a number of structural features observed within the fault systems such as tiers of faults the location of maximum fault throw and growth components at upper fault tips as such this paper represents the first attempt to correlate microscale properties of clay rich sediments to their macroscale seismic character

discussion on development of polygonal fault systems a test of hypotheses d m d james writes the mechanics of formation of polygonal faults are widely acknowledged as not yet fully understood and it is welcome that goulty swarbrick 2005 attempt a discriminatory test between rival hypotheses it is however important that such a test bears some relation to physical reality the test is based on the assumption that the ratio of horizontal to vertical effective stress as deduced from leak off tests in two wells in the north sea at depths of about 2 km yields the co efficient of earth pressure at rest therein and hence the residual friction governing the post nucleation development of polygonal faults apparently globally and at any depth it is not clear if the authors consider that the polygonal fault tiers at the well sites are currently active neither is it clear if they assume that the coefficient of residual friction along the fracture is a reasonable approximation to the coefficient of initial friction which governs the dip of the propagating fracture tip and the fault surface as a whole relative to the orientation of the vertical effective stress it is hardly surprising that the ratio of horizontal to vertical effective stress k is very high in the wells analysed the leak off tests are from highly overpressured horizons ratios of pore fluid pressure to total vertical stress approximately 0 80 and 0 84 and the effect of pore fluid pressure coupling hillis 2003 will inevitably decrease the value of the horizontal effective stress to lesser extent than it does the vertical effective stress it is certainly not yet demonstrated that polygonal faults require overpressures of this magnitude for their formation by any mechanism leak off tests tend to overestimate the horizontal effective stress if no correction is made for the excess mud pressure necessary to overcome the tensile strength of

polygonal faults and their implications for hydrocarbon reservoirs in the southern qiongdongnan basin south china sea the polygonal faults were identified in qiongdongnan basin south china sea by using the technique of time coherent slice and horizon flattening of high resolution 3d seismic data these polygonal faults occur in three tiers of the upper meishan formation and the huangliu formation the faults have lengths of 150 1500 m spacings of 50 3000 m throws of 10 40 m and dips of 50 90 degrees tectonic evolution in the qiongdongnan basin can be divided into a rifted stage and a post rifted stage tectonic faults are widely distributed in the rifted sequences but are not well developed in the post rifted stage few faults in the post rifted sequences might suggest the absence of a migration pathway for hydrocarbon or other fluids however the existence of polygonal faults in the post rifted sequences can serve as the pathway and promote the hydrocarbon migration and accumulation in the qiongdongnan basin during the post rifted stage c 2010 elsevier ltd all rights reserved

discrimination of uxo in soil using broadband polarimetric gpr backscatter polarimetric analysis of ground penetrating radar gpr backscatter offers a new means of discriminating subsurface metallic target shapes from one another such discrimination is urgently needed to distinguish buried unexploded ordnance uxo from other subsurface objects to illuminate the underlying phenomenology of scattering from objects enveloped in soil three dimensional 3d simulations are performed over a broad frequency band characteristic of new low frequency gprs for moist soil this means that the subsurface wavelength may range from a fraction of the target size to an order of magnitude larger with a transmitting antenna representation that produces typical subsurface gpr beam features combined effects of positional orientation and frequency diversity are investigated despite long wavelengths results show distinctive features in reflections obtained from contrasting example target shapes full polarimetric analysis suggests the capability for inferring the length of elongated targets aspect ratio and rotational symmetry and gross shape along the axis for either elongated or flattened bodies of revolution in problematical orientations

in search of ice stream sticky spots the form drag of large bedrock bumps sticking into the base of an ice stream can produce effective sticky spots supporting large basal shear stress bedrock regions surrounded by lubricating till at the same topographic level can cause sticky spots but tend to collect lubricating water and thus are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps raised regions on the ice air surface also can cause moderate increases in the shear stress supported on the bed beneath surveys of large scale bedrock roughness strain grids across the margins of ice surface highs and possibly water pressure measurements in regions of thin or zero till would help identify and characterize sticky spots

physical properties and rock physics models of sediment containing natural and laboratory formed methane gas hydrate this paper presents results of shear strength and acoustic velocity p wave measurements performed on 1 samples containing natural gas hydrate from the mallik 2l 38 well mackenzie delta northwest territories 2 reconstituted ottawa sand samples containing methane gas hydrate formed in the laboratory and 3 ice bearing sands these measurements show that hydrate increases shear strength and p wave velocity in natural and reconstituted samples the proportion of this increase depends on 1 the amount and distribution of hydrate present 2 differences in sediment properties and 3 differences in test conditions stress strain curves from the mallik samples suggest that natural gas hydrate does not cement sediment grains however stress strain curves from the ottawa sand containing laboratory formed gas hydrate do imply cementation is present acoustically rock physics modeling shows that gas hydrate does not cement grains of natural mackenzie delta sediment natural gas hydrates are best modeled as part of the sediment frame this finding is in contrast with direct observations and results of ottawa sand containing laboratory formed hydrate which was found to cement grains waite et al 2004 it therefore appears that the microscopic distribution of gas hydrates in sediment and hence the effect of gas hydrate on sediment physical properties differs between natural deposits and laboratory formed samples this difference may possibly be caused by the location of water molecules that are available to form hydrate models that use laboratory derived properties to predict behavior of natural gas hydrate must account for these differences

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

episodic basin wide fluid expulsion from geopressured shale sequences in the north sea basin a proposed general model for the episodic dewatering of thick shale successions is based on the recognition of a pervasive polygonal extensional fault network developed in the dominantly fine grained lower tertiary of the north sea basin seismic data show that the faults are arranged in stratigraphically bound structural units tiers that are delimited vertically by almost undeformed condensed sections and are restricted in distribution to the lowest permeability slope and basin floor facies i propose an episodic three stage mechanism to explain the fault genesis involving 1 the development of basin wide overpressured compartments 2 a density inversion between the overpres sured units and the overlying seal and 3 natural hydraulic fracturing pressure bleed off and resealing of the pressure compartment leading to a repeat of the cycle

radar polarimetry analysis applied to single hole fully polarimetric borehole radar a fully polarimetric borehole radar system using four combinations of dipole and slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes first to implement radar polarimetry analysis a processing scheme suitable for analyzing a single hole reflection data set acquired by the system is presented this processing consists of antenna characteristic compensation migration for image reconstruction and time frequency analysis for single frequency data set construction two polarimetric target decomposition methods namely 1 pauli decomposition and 2 eigenvector based decomposition are applied to characterize the scattering problem of the subsurface fractures the pauli decomposition method provided important radar polarimetry information of fractures and the eigenvector based decomposition method made a significant contribution to understanding the scattering mechanisms from different fractures with different properties furthermore information about fracture classification can be obtained by analysis of the h alpha distribution provided by eigenvector based decomposition of local radar image regions the potential of polarimetric target decomposition techniques to fracture characterization is shown which in turn provides valuable information about water permeabilities of fractures in hydrogeological studies

development of polygonal fault systems a test of hypotheses polygonal networks of normal faults in layer bound sequences of fine grained mudstones have formed without regional tectonic extension the two leading hypotheses concerning the generic mechanism responsible for their development are 1 horizontal stresses are reduced by syneresis 2 coefficients of residual friction are very low to discriminate between these hypotheses the ratios between the minimum horizontal and the vertical effective stresses have been estimated in four north sea wells penetrating oligocene and miocene sequences that contain polygonal fault networks the effective stress ratios are c 0 8 consistent with very low coefficients of friction but not with syneresis

identification of a large upper cretaceous polygonal fault network in the hammerfest basin implications on the reactivation of regional faulting and gas leakage dynamics sw barents sea abstract we use a high resolution 3d seismic dataset covering 970 km2 over the snohvit and albatross gas fields of the hammerfest basin in the barents sea in order to investigate the basin fault architecture and identify potential fluid pathways of deeper thermogenic gas and fluids a polygonal fault pf interval not previously published is described in the three non connected blocks within campanian sequences which could imply a permeable complex network of pathways that facilitate the vertical migration of hydrocarbons along the fault planes the dominant orientation of the pfs is similar to the main regional tectonic fault trend ew suggesting a tectonic influence upon the development of polygonal faults although some individual pfs locally seem to develop orthogonally to regional 1st order tectonic faults a lithologic control on the occurrence of pf patterns is evident as none are observed within calcareous low clay sediments the pf networks present three main orientations dominant ene wsw secondary nne ssw and a minor ne sw paleocene early eocene faults peefs prevail above the pf networks with coinciding ene wsw fault strikes interpreted as preferential reactivation of the pf systems numerous amplitude anomalies linked to the escape of thermogenic fluids from the jurassic reservoir were identified we present a conceptual model where the 1st order reactivated faults and peefs acted as pathways for fluids from the deeper hydrocarbon reservoirs the peefs are partially sealing with a lateral migration component interplay between the pfs peefs and the 1st order reactivated faults focuses the fluids vertically along the polygonal fault traces creating a wider diffuse zone which form large gas cloud anomalies in the seismic data

small scale faulting in the upper cretaceous of the groningen block the netherlands 3d seismic interpretation fault plane analysis and regional paleostress abstract over the last years field based studies have shown that fault surfaces can exhibit a considerable self affine topography it is reasonable to assume that similar undulations are also present in fault interpretations from 3d reflection seismic data however both the interpretation uncertainty and geophysical resolution limits hinder their analysis this study analyses a set of small scale non reactivated faults in the upper cretaceous chalk group upper ommelanden formation of the nw part of the groningen block the netherlands in a high quality pre stack depth migrated 3d seismic data set the studied faults are fully contained inside the chalk group in an area located between the major tectonic bounding faults of the nw groningen block over 200 faults with offsets in the order of 30 50 m were interpreted across an area of ca 150 km 2 showing a clear preferential orientation for strike dip and dip direction detailed interpretations and 3d fault plane analyses show undulations on the fault plane we show that these undulations are not an interpretation or gridding artefact and interpret these to indicate direction of fault slip these results were used to calculate a paleostress tensor using all faults to calculate a single stress tensor for the entire study area by numerical dynamic analysis based on the orientation position and a thickness analysis it is interpreted that these faults formed due to the tectonic reactivation of salt structures in the latest cretaceous the calculated paleostress state shows a general nw se extension with a vertical maximum principle stress and a stress ratio of about 0 3 indicating that the studied faults are not the result of dewatering this interpretation agrees both with a nearby salt tectonic reconstruction as well as field based paleostress results from the uk belgium and france a first look at other surveys from the dutch sector indicates that similar faults are present in other areas with different orientations we propose that a dedicated analysis of these faults across on and offshore europe would allow extending the stress map of the late cretaceous into areas where the chalk is not outcropping

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

side scan targets in lake superior evidence for bedforms and sediment transport a high resolution side scan sonar survey of the lake bed off the keweenaw peninsula lake superior demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m numerous lineations which run parallel to the shore appear to be sand ribbons a field of sedimentary furrows which occurs in one area demonstrates the long term directional stability of the near bottom flow large 100 300 m in diameter 2 5 m deep unusual ring like or arcuate depressions are common throughout the western half of lake superior these rings themselves do not appear to have been formed by bottom currents but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed off the keweenaw peninsula the forms of the rings have been modified by bottom currents the bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

basal shear stress of the ross ice streams from control method inversions 1 we used control method inversions to determine the basal shear stress beneath the ross ice streams where new high resolution velocity data sets have recently become available the inversion algorithm was adapted from an earlier viscous bed algorithm to allow solution for the basal shear stress corresponding to a weak plastic bed we performed several experiments using synthetic data to determine the quality of the inversions these experiments indicate that with high quality surface elevation data e g errors 5 m the inversions are relatively robust with respect to errors in ice flow velocity and bed topography the inversions are consistent with seismic and borehole observations and indicate that the ross ice streams lie atop a bed that is nearly everywhere weak in contrast the tributaries feeding these ice streams overlie alternating patches of strong and weak bed

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

regional jointing in the northern michigan basin the orientations of joints were measured at 142 locations across the northern michigan basin in rocks of cambrian to devonian age four major vertical joint sets were found throughout the area the average trends of the four sets are 052 134 091 and 001 there are small random fluctuations in mean orientation of all the sets but they remain remarkably consistent in orientation throughout the area across lithologic and stratigraphic boundaries and across a regional strike change around the michigan basin of about 115 the joint pattern does not seem to be related to structural trends in the precambrian basement inferred from geophysical data the joint set at 134 has the same trend as a series of major folds in the paleozoic rocks of the michigan basin suggesting that this joint set may be related to the folding the joint set at 052 is parallel with the maximum horizontal compressive stress that exists today throughout the mid continent region this joint set may be extension joints formed in response to the present stress regime

bedrock jointing and geomorphology in southwestern ontario canada an example of tectonic predesign in southwestern ontario canada palaeozoic sedimentary strata are covered by pleistocene glacial sediments the topography of the buried bedrock surface has been mapped over an area of some 45 000 km2 using new computerised depth to bedrock data from more than 200 000 waterwells this information shows that arching of the underlying proterozoic basement canadian shield and differential erosion of carbonate and shale strata are first order regional controls on bedrock geomorphology these data also define a network of buried bedrock channels quantitative analysis of the trends of these channels reveals a statistical correspondence between channel orientation and regional bedrock joint sets formed in response to the mid continent stress field the orientations of bedrock channels and joints correspond regionally with mean trends at 153 and 164 respectively in addition two dominant orientations of postglacial river valleys and bedrock joints correspond with mean trends at 104 vs 104 and 54 vs 52 respectively our findings show that the erosional channelled topography cut on bedrock together with the postglacial drainage pattern cut into younger glacial sediments are related to the trend of bedrock joints and consequently can be described as tectonically predesigned in addition this study yields new insights into the form of the preglacial tertiary drainage system in southern ontario prior to pleistocene glaciation regardless of the precise age of this preglacial system and degree of subsequent glacial modification an important factor in its geomorphic development has been the mid continent stress field

response of subglacial sediments to basal freeze on 1 theory and comparison to observations from beneath the west antarctic ice sheet 1 we have constructed a high resolution numerical model of heat water and solute flows in sub ice stream till subjected to basal freeze on the model builds on quantitative treatments of frost heave in permafrost soils the full version of the clapeyron equation is used hence ice water phase transition depends on water pressure osmotic pressure and surface tension the two latter effects can lead to supercooling of the ice base this supercooling in turn induces hydraulic gradients that drive upward flow of pore water which feeds the growth of segregation ice onto the freezing interface this interface may progress into the till and form ice lenses if supercooling is sufficiently strong hence the ice segregation process develops a stratified basal ice layer in our model a high basal temperature gradient 0 054 c m 1 triggers ice stream stoppage and the loss of basal shear heating leads to relatively high basal freeze on rates 3 5 mm a 1 in response the subglacial till experiences comparatively rapid consolidation till porosity can decrease from 40 to 120 kpa approximately within one century basal supercooling arising from redistribution of solutes and ice water interfacial effects amounts to ca 0 35 c below the pressure melting point fine grained till is in our model associated with widely spaced thick ice lenses coarse grained till yields thinner ice lenses that are more closely spaced our model results compare favorably although not in all details with available observational evidence from borehole studies of west antarctic ice streams

rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion contrary to what has recently been assumed in modeling the proposed deforming bed mechanism for the rapid motion of antarctic ice streams the rheology of water saturated till is probably highly nonlinear according to information from soil mechanics and preliminary experiments on till from the base of ice stream b the equivalent flow law exponent n is probably as high as 100 and the nonlinearities of the shear stress and effective pressure dependences are closely linked the high nonlinearity has important consequences for the deforming bed mechanism a flow system operating by this mechanism can be unstable as a result of feedback from the generation of basal water by shear heating of basal till the short term feedback effect is analyzed for a perturbation in a model ice stream in which the basal meltwater is transported through a distributed system of narrow gap conduits at the ice till interface although the analysis is approximate and some of the system parameters are poorly known the results suggest that the deforming bed mechanism is unstable for n 20 the apparent lack of such an instability in the currently active ice streams implies that their motion is controlled not by the deforming bed mechanism but by some other as yet unidentified mechanism

prediction of 3 d fluid permeability and mudstone distributions from ground penetrating radar gpr attributes example from the cretaceous ferron sandstone member east central utah a 3 d fluid permeability distribution is estimated inside a channel sandstone reservoir analog in the cretaceous ferron sandstone fluvio deltaic complex in east central utah from ground penetrating radar gpr attributes fluid permeability measurements at 5 cm spacing along four boreholes and one pseudohole section at the adjacent cliff face are used together with instantaneous amplitude and frequency attributes of gpr data to predict fluid permeabilities away from the measured vertical transects and to delineate the distribution and geometry of mudstone layers inside the reservoir analog statistically significant relationships are determined between the well data fluid permeability and mudstone content and the gpr attributes these calibrations are applied to the entire gpr volume to estimate the 3 d fluid permeability variation and the lateral development of mudstone units measured and predicted fluid permeabilities range from 0 1 to 290 md one of the five units considered contained no mudstone lay

geomorphology under ice streams moving from form to process ice streams are integral components of an ice sheet s mass balance and directly impact on sea level their flow is governed by processes at the ice bed interface which create landforms that in turn modulate ice stream dynamics through their influence on bed topography and basal shear stresses thus ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics this paper reviews developments in our understanding of ice stream geomorphology from an historical perspective with a focus on the extent to which studies of modern and palaeo ice streams have converged to take us from a position of near complete ignorance to a detailed understanding of their bed morphology during the 1970s and 1980s our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in antarctica very few palaeo ice streams had been identified with any confidence during the 1990s however glacial geomorphologists began to recognise their distinctive geomorphology which included distinct patterns of highly elongated mega scale glacial lineations ice stream shear margin moraines and major sedimentary depocentres however studying relict features could say little about the time scales over which this geomorphology evolved and under what glaciological conditions this began to be addressed in the early 2000s through continued efforts to scrutinise modern ice stream beds at higher resolution but our current understanding of how landforms relate to processes remains subject to large uncertainties particularly in relation to the mechanisms and time scales of sediment erosion transport and deposition and how these lead to the growth and decay of subglacial bedforms this represents the next key challenge and will require even closer cooperation between glaciology glacial geomorphology sedimentology and numerical modelling together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams

submarine glacial landforms and rates of ice stream collapse the rate of deglacial ice sheet retreat across polar continental shelves and possible ice stream collapse and sea level rise has been much debated high resolution imagery of seafloor morphology is available for many polar shelves and fjords the rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms produced at ice stream sedimentary beds these landforms exposed by ice retreat across high latitude shelves demonstrate that deglaciation occurs in three main ways rapidly by flotation and breakup episodically by still stands and or grounding events punctuating rapid retreat or by slower retreat of grounded ice submarine landform assemblages imply through the presence of grounding zone wedges overprinting mega scale glacial lineations on many polar shelves that ice stream retreat is more often episodic than catastrophic these observations provide a robust test of the ability of numerical models to predict the varied response of ice sheet basins to environmental changes

ice thrust features and the maymont landslide in the north saskatchewan river valley the battleford glacier created shearing and softening of bedrock clays contributing to widespread slope instability along the valley of the north saskatchewan river the battleford glacier flowed southeastward down the valley of the north saskatchewan river during its final stage in west central saskatchewan it created flutings crevasse fillings folding and faulting in ice thrust ridges and extensive horizontal gouge zones filled with soft malleable clay extensive drilling and testing for the foundations of the maymont bridge provided definitive data outlining at least three gouge zones the shallowest gouge zone at an elevation of 465 m defines the base of the most severe glacial folding and deformation of the bedrock in at least one of the ice thrust ridges the deeper gouge zones are at about 433 and 438 m elevation postglacial landslides slumps along the southern side of the north saskatchewan river are controlled by the gouge zones which are low friction slide surfaces along which large ho

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

ultrawide bandwidth fully polarimetric ground penetrating radar classification of subsurface unexploded ordnance an ultrawide bandwidth uwb ground penetrating radar gpr was used to collect fully polarimetric backscattered data from 10 to 800 mhz using a dual polarization version of the previously developed dielectric loaded horn fed bow tie hfb antenna special processing algorithms were developed to extract the polarization orientation depth and length features of the target under investigation the polarization and resonance features were utilized to discriminate subsurface ordnance from false alarm objects that do not have elongated bodies the classification of a specific type of unexploded ordnance uxo was also performed using the known length information the processed results obtained from an initial blind field test show a very encouraging discrimination performance

tectonic controls on the genesis and distribution of late cretaceous western interior basin hydrocarbon seep mounds tepee buttes of north america abstract within the western interior basin of north america hundreds of small carbonate mounds associated with late cretaceous hydrocarbon emissions or seeps form the most extensively distributed occurrence of fossil seep mounds that is known the tepee buttes analysis of the stratigraphic literature for the basin reveals that tepee butte formation occurred intermittently over a 10 m yr period within a narrowly restricted paleogeographic region the modern geographic distribution of the tepee buttes is constrained roughly to between 101 30 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empt

measurement of diagenetic compaction strain from quantitative analysis of fault plane dip we developed a new technique for quantifying the amount of porosity loss during diagenetic transformation of opal a to opal ct the technique is based on 3d seismic data from offshore norway where the widely developed biosiliceous sediments of the brygge formation are deformed by a polygonal fault system evidence is shown from two study areas that the dip of the polygonal fault planes reduces abruptly across the opal a to opal ct diagenetic boundary suggesting that the fault planes were passively rotated into shallower dips due to diagenesis the reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis using an independent assessment of the magnitude of the porosity loss we are able to validate the method based on fault plane dips and also to evaluate whether the porosity loss results in an exclusively vertical strain additionally the impact of silica diagenesis on the shear strength of the sediments and fault growth is investigated we present evidence suggesting that deviations from classical mohr coulomb behaviour may be expected during the combined processes of diagenesis and porosity collapse and may indeed be sufficient to promote continued fault growth

response of subglacial sediments to basal freeze on 2 application in numerical modeling of the recent stoppage of ice stream c west antarctica 1 ross ice streams supply over 90 of the ice volume flowing out of the ross sector of the west antarctic ice sheet wais stoppage of ice stream c isc ca 150 years ago appears to have pushed this sector of wais from negative into positive mass balance joughin and tulaczyk 2002 we propose an explanation for the unsteady behavior of isc using a new numerical ice stream model which includes an explicit treatment of a subglacial till layer when constrained by initial conditions emulating prestoppage geometry dynamics and mass balance of isc the model yields a rapid 100 years stoppage of the main ice stream trunk the stoppage is triggered by basal freeze on which consolidates and strengthens the subglacial till our numerical simulations produce results consistent with a number of existing observations for example continuing activity of the two tributaries of isc the model always yields rapid stoppage unless we specify ice stream width that is smaller than its prestoppage values maximum of 80 km we conjecture that if isc was active for at least a few thousand years before slowdown its width was significantly smaller than today to sustain the long active phase ice stream width is a key control that helps determine whether ice stream flow is sustainable over a long term our work indicates that the recent stoppage of ice stream c could have been part of inherent ice stream cyclicity and it leaves open the possibility that other active ice streams may evolve in the future toward rapid shutdowns

structurally controlled diagenesis of a carbonate ramp banff formation alberta canada abstract the lower carboniferous banff formation represents a homoclinal carbonate ramp its layer cake geometry and homogeneous lithology over a large area make it ideal to study palaeostructures and palaeofault systems the study of 607 wells in the area east of jasper park outlines major diagenetic features that are probably structurally related in each well the average lithology has been broken down into limestone dolomite and shale with the dolomite content and the porosity being mapped because of the varying density of wells an anomaly mapping technique has been used that is based on flagging anomalies wells outside the norm after searching in six out of eight octants the contour maps indicate that anomalous zones of porosity and oil stain migration pathways are related to dolomitisation trends their linear geometry and their location indicate a structural control three major trends nw se ne sw and nne ssw are recognised they have varying characteristics comparison of the anomaly maps for dolomite and porosity shows locally a typical pattern of overdolomitisation in the ne sw trends assessment of the relative timing of the various dolomitisation and porosity phases has been tentatively made in one case a lateral throw of a previously non recognised fault has been measured 65 km a comparison with known devonian sedimentary and diagenetic features is tentatively made in order to validate the outlined trends and their interpretations

shallow faults upper cretaceous clinoforms and the colonsay collapse saskatchewan reflection seismic data in the vicinity of the colonsay potash mine near saskatoon saskatchewan reveal numerous shallow normal faults with vertical displacements of as much as 25 m the faults cut the glacial deposits and upper cretaceous rocks to a maximum depth of about 400 m horizontal length ranges from a few hundred to a few thousand metres similar faults are also exposed in several widely separated open pit coal mines of southern saskatchewan and may be common elsewhere in the prairies such faulting is considered to be a result of tertiary to quaternary extensional tectonics and may have been aided in this region by the melting of gas hydrates the study area includes the east flank of the colonsay collapse a subsidence structure caused by dissolution and removal of salt in the 200 m thick devonian prairie evaporite formation salt was removed in two stages prior to or during early glacial time and in late glacial time subsidence was gradual with no observable faulting a complex of clinofor

ice sheet dynamics and ice streaming along the coastal parts of northern norway abstract in this paper regional and high resolution bathymetric data are used to reconstruct the pattern and dynamics of ice sheet flow in the fjord and shelf areas of northern norway interpretation of the morphology of the sea floor reveals a series of glacigenic features which are mainly related to the most recent glaciation of the area the shelf area of troms county comprises four cross shelf troughs with intermediate shallow banks glacial features within the cross shelf troughs mega scale glacial lineations msgl lateral shear margin moraines grounding zone wedges are interpreted to have been formed under fast flowing ice streams on the shallow bank areas there are far fewer ice flow indicators and here relatively passive ice acted as interstream ridges outside the finnmark coast to the north and east a coast parallel depression djuprenna deflected rapidly flowing ice from the fjords in a generally east to west direction and then farther out through ingoydjupet and into the bear island trough the fjords guided most of the ice flow and functioned as tributaries to the major ice streams on the shelf including the vast bear island trough ice stream at the last glacial maximum the landform distribution and their cross cutting relationships indicate that major switches in ice stream flow direction took place during deglaciation additionally grounding zone wedges are found within the cross shelf troughs and these reveal temporal variability in ice stream dynamics in different troughs during deglaciation the distribution of glacigenic features on the ice stream beds also reveals a downstream evolution that has been reported by other workers whereby small bedrock features progressively merge into more elongate forms and msgl this downstream evolution in subglacial geology subglacial bedforms implies that the force balance e g basal shear stress of the ice streams also evolves in the downstream direction and more crucially that the flow mechanism of the ice stream is spatially variable along its length

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

influence of stratigraphic setting and simple shear on layer bound compaction faults offshore mauritania abstract we have used three dimensional seismic data to examine the geometry of layer bound compaction faults on the mauritanian continental margin the faults deform a fine grained neogene unit which mantles buried canyons above the canyons most layer bound faults strike perpendicular to the canyon axes whereas adjacent to the canyons the faults are omni directional and intersect bedding planes in polygonal patterns on the flanks of a large structural high faults also strike perpendicular to the slope direction displaying a concentric pattern faults that show preferential alignment are located in areas with increased bedding dip and most aligned faults are antithetic to the bedding dip where the bedding dip is greater than 1 the synthetic faults dip more steeply than the antithetic faults this discovery was unexpected because the stress tensor due to the effect of gravity on a dipping margin would cause the antithetic faults to form with steeper dips which we show theoretically we hypothesise that the layer hosting the faults has been subjected to simple shear of 20 or more with the top of the layer displaced downdip by 100 m relative to its base a potential application of these and similar observations is to assess slope stability on continental margins

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

iceberg scours pits and pockmarks in the north falkland basin abstract glaciation in the southern hemisphere is limited by the availability of land from which to seed ice sheets the extents of the antarctic patagonian and new zealand ice sheets at the last glacial maximum lgm are relatively well known although the rates and styles of their retreat after the lgm are poorly constrained particularly in antarctica offshore records of glaciation are relatively sparse in the southern hemisphere despite the potential ocean climate insights that can be gained from records of glaciation that are preserved offshore in this study we document the occurrence of iceberg scours and accompanying pits within the north falkland basin c 50 s and discuss their origin the cross sectional shapes of scours are u to v shaped and occur in present day water depths of 280 to 460 m individual scours are up to 38 km long 1 km wide and up to 10 m deep the scours are observed as erosional linear to curvilinear depressions showing only one point of contact between the iceberg and seafloor often with raised berms composed of excavated material identified either side of the main depression undulating width of scours is interpreted as an effect of rotation of the iceberg keel during scour excavation the elongate morphology of the scours differentiates them from asymmetrical pits interpreted to represent iceberg impact pits and symmetrical pockmarks interpreted to form due to fluid expulsion in cross section the differentiation is highly interpretative but the 3d bathymetric expression is unequivocal the sinusoidal character of the scours suggests the interaction between local tidal currents and the east falkland malvinas currents in the north falkland basin at the time of formation offshore and onshore landscape analysis is used to determine potential sources of icebergs and suggests that they were most likely sourced from the antarctic peninsula these results inform our understanding of southern hemisphere ocean climate interactions during the last glacial cycle and suggest that the east falklands malvinas current a key current in the southern hemisphere bringing cold low salinity antarctic derived waters into the south atlantic was in operation during the last glacial cycle the accumulation of icebergs west of the falkland islands would also result in further cooling from fresh meltwater perturbations enhancing the development of a potential ice bridge along the argentinian coast

methane hydrate in crystalline bedrock and explosive methane venting tectonics abstract methane hydrate clathrate ice does not only form in shelf environments but may also accumulate in voids and fractures in continental crystalline rocks this has turned out to be the case in formerly glaciated areas where the waxing and waning of thick ice caps following the quaternary alterations between ice ages and interglacial implied very large changes both in temperature and pressure in the bedrock below the swedish situation is highlighted seepage of methane gas from the crystalline bedrock is recorded methane accumulated as ice in fractures and voids in the rock in postglacial time such accumulations vented explosively generating methane venting tectonics this occurred both spontaneously as a function of changes in temperature and load pressure and partly as violent deformational events as a function of earthquake events whilst most venting events refer to the time of deglaciation three major deformational events occurred shortly after the uplift induced land emergence in late holocene time a possible analogous event in association with the 1988 saguenay earthquake in canada is revisited

visualization of active faults using geometric attributes of 3d gpr data an example from the alpine fault zone new zealand three dimensional ground penetrating radar gpr data are routinely acquired for diverse geologic hydrogeologic archeological and civil engineering purposes interpretations of these dataareinvariablybasedonsubjectiveanalysesofreflectionpatterns such analyses are heavily dependent on interpreter expertiseandexperience usingdataacquiredacrossgravelunitsoverlyingthealpinefaultzoneinnewzealand wedemonstratethe utilityofvariousgeometricattributesinreducingthesubjectivity of3dgprdataanalysis weuseacoherence basedtechniqueto compute the coherency azimuth and dip attributes and a graylevel co occurrence matrixglcmmethod to compute the texture basedenergy entropy homogeneity andcontrastattributes a selection of the gpr attribute volumes allows us to highlight key aspects of the fault zone and observe important features not apparent in the standard images this selection also provides information that improves our understanding of gravel deposition andtectonicstructuresatthestudysite anewdepositional structuralmodellargelybasedontheresultsofouranalysisofgprattributes includes four distinct gravel units deposited in three phases and a well defined fault trace this fault trace coincides with a zone of stratal disruption and shearing bound on one side by upward tilted to synclinally folded stratified gravels and on the other side by moderately dipping stratified alluvial fan gravelsthatcouldhavebeenaffectedbylateralfaultdrag whenused in tandem the coherence and texture based attribute volumes can significantly improve the efficiency and quality of 3d gpr interpretation especially for complex data collected across activefaultzones

three dimensional consolidation of fine grained sediments current theories of one to three dimensional consolidation are based on the concept of gravitational loading with concomitant expulsion of pore fluid as a result of mechanical rearrangements of particles and porosity reduction however the recent discovery of extensive networks of layer bound fractures forming polygonal patterns in extremely fine grained smectitic clays and chalks suggests that current theory may not adequately explain the consolidation process in such sediments these faults develop during shallow burial and often appear to have been active at the sediment water interface radially isotropic strain suggests that the process of formation was nontectonic measured values of strain suggest that deformation resulted from volumetric contraction of the sediments we argue that the formation mechanism for these fault systems is related to the colloidal properties of the constituent sediments and that as such stresses due to gravity may not be the only factor controlling pore fluid expulsion

a late cretaceous polygonal fault system in central north america polygonal fault systems pfs have been interpreted worldwide using seismic data imaging sedimentary strata normal faults initiate over a large area in fine grained subaqueous strata soon after deposition as they continue to grow laterally and vertically their fault traces intersect to form polygons in plan view these polygons are difficult to image without three dimensional 3 d seismic data the faulting is initiated during sediment dewatering and mud particle consolidation that can be independent of external stresses in the past 20 years hundreds of basins worldwide have been interpreted to contain polygonal faults this paper presents a pfs interpretation for fine grained sediments deposited in the late cretaceous western interior seaway of the great plains of north america the faulted strata have been observed as a pfs at depths ranging from 2750 m subsurface to outcrop seismic dataset interpretations and borehole analyses corroborate previously published outcrop analyses and seismic interpretations the larger observed faults are mesoscale in size with throws up to 80 m and strike lengths up to 1 5 km potentially encompassing over 2 000 000 km 2 observational averages imply 10 7 or more mesoscale size faults with an order of magnitude greater number of smaller faults at shallow depth and outcrop the pfs model of extensive normal faulting could help to explain late cretaceous shale faulting attributed to other causes such as deeper sediment dissolution or glacial processes in the subsurface faulting and fracturing consistent with a pfs model can help to explain fault geometries observed in well control and 3 d seismic data

using gpr data as constraints in rmt data inversion for water content estimation a case study in heby sweden this study uses ground penetrating radar gpr data as constraints in the inversion of radio magnetotelluric rmt data to provide an improved model at shallow depth we show that modification of the model regularization matrix using all gpr common offset co reflections can mislead the constrained inversion of rmt data to avoid such problems common mid point cmp gpr data are translated to a resistivity model by introducing a new petrophysical relationship based on a combination of topp s and archie s equations this model is updated through a semi iterative method and is employed as an initial and prior model in the subsequent inversion of rmt data finally a water content model that fits the gpr cmp and rmt data is derived from the resistivity model computed by the constrained inversion of rmt data to assess the proposed scheme it is applied to a synthetic data set then real rmt data collected along an 870 m long profile across a known aquifer situated in the north of heby central sweden are inverted by removing the smoothness constraints across gpr co interfaces or using cmp based inversion thick 10 m vadose and saturated zones are resolved and shown to correlate with logs from nearby boreholes nevertheless the application of our cmp based inversion was the only efficient scheme to retrieve thin 3 m saturated zones and the water table at a depth of 7 15 m in the rmt models the estimated models of water content are in good agreement with the available hydrogeological information in the study area

subglacial water storage and drainage beneath the fennoscandian and barents sea ice sheets abstract subglacial hydrology modulates how ice sheets flow respond to climate and deliver meltwater sediment and nutrients to proglacial and marine environments here we investigate the development of subglacial lakes and drainage networks beneath the fennoscandian and barents sea ice sheets over the late weichselian utilizing an established coupled climate ice flow model we calculate high resolution spatio temporal changes in subglacial hydraulic potential from ice sheet build up 37 ka bp to complete deglaciation 10 ka bp our analysis predicts up to 3500 potential subglacial lakes the largest of which was 658 km2 and over 70 of which had surface areas

great plains polygonal fault system as expressed in saskatchewan late cretaceous fault initiation and graben formation an extensive polygonal fault system pfs has been recognized in fine grained late cretaceous sediments of the western interior seaway of north america polygonal fault systems are pervasive organizations of nontectonic faults with fault traces that coalesce to form distinctive polygonal fault patterns interpretation of a three dimensional seismic dataset from southeast saskatchewan provides insight into fault initiation timing and geometry for the great plains pfs gppfs faulting initiates in the niobrara formation with the largest fault throws occurring over early cretaceous viking formation sandstone accumulations suggesting that drape compaction over the channel sand initiated some of the faulting above this faulting increases in vertical offset and the predominant fault strike angles change in the lea park belly river and bearpaw formations all homotaxial to the pierre shale throughout campanian time by late bearpaw time the initially almost random fault strike orientations change to well defined northwest southeast and west east striking grabens these grabens have up to 20 m of throw and can be 125 m wide and 900 m long at 400 m current depth predominant graben faults are the continuation of some of the deeper pfs faults moreover the grabens are present over a campanian clinoform bed and may be interpreted to indicate bearpaw time extension tectonics that is local or regional in scale the pfs helps to explain near surface faulting observed in late cretaceous sediments in the western interior seaway and could be used as a model to help explain late cretaceous geology subsurface groundwater flow and shallow natural gas reservoir continuity

geotechnical engineering significance of great plains polygonal fault system an extensive polygonal fault system pfs within fine grained upper cretaceous sediments beneath the great plains of north america has implications for geotechnical engineering geological well con

ice stream flow switching during deglaciation of the southwestern barents sea ice streams dominate the discharge of continental ice sheets recent observations and reconstructions have revealed that large scale reorganizations in their flow trajectory flow switching can occur over relatively short time scales however the underlying causes of such behavior and the extent to which they are predictable are poorly known this paper documents a major episode of ice stream flow switching during the late weichselian deglaciation of the southwestern barents sea and explores various hypotheses for its causation regional bathymetric data show that two ice streams that had similar adjoining topographically constrained source areas had very different trajectories and dynamics on the outer shelf at the late weichselian maximum the hakjerringdjupet ice stream flowed westward along the cross shelf trough of hakjerringdjupet while the soroya trough ice stream flowed northward into ingoydjupet forming a tributary of the bjornoyrenna ice stream initial retreat of the hakjerringdjupet ice stream was rapid but with episodic periods of grounding as it retreated onto the higher rougher topography of the inner shelf we infer a reduction in ice velocity and a dramatic decrease in the pace of retreat as recorded by nested sequences of recessional moraines following and probably in response to this we suggest that there was a short lived surge readvance of an adjacent lobe onto fugloybanken in contrast the adjacent soroya trough ice stream remained active throughout deglaciation before retreating rapidly with no stillstands or readvances we argue that the different retreat histories of the ice streams were determined by variations in bed topography bathymetry which modulated the grounding line response to sea level variation such a mechanism is likely to be an important control on the long term behavior of marine based ice streams and outlet glaciers in antarctica and greenland and suggests that gathering data on their subglacial topography should be a priority

combination of h alpha decomposition and migration for enhancing subsurface target classification of gpr polarimetric technology has been one of the most important advances in microwave remote sensing during recent decades h alpha decomposition which is a type of polarimetric analysis technique has been common for terrain and land use classification in polarimetric synthetic aperture radar however the technique has been less common in the ground penetrating radar gpr community in this paper we apply the h alpha decomposition to analyze the surface gpr data to obtain polarimetric attributes for subsurface target classification also by combining h alpha decomposition and migration we can obtain a subsurface h alpha color coded reconstructed target image from which we can use both the polarimetric attributes and the geometrical features of the subsurface targets to enhance the ability of subsurface target classification of surface gpr a 3 d full polarimetric gpr data set was acquired in a laboratory experiment in which four targets a scatterer with many branches a ball a plate and a dihedral scatter were buried in dry sand under flat ground surface and used to test these techniques as results we obtained the subsurface h alpha distribution and classified the subsurface targets also we derived a subsurface h alpha color coded reconstructed target image and identified all four targets in the laboratory experiment

displacement field in contraction driven faults we investigate the distribution of strain and deformation in the host sediment that arises once a contraction driven shear fault has localized and propagated under a zero lateral strain condition numerical modeling of displacement distributions compares well with those measured using 3d seismic data the parameters that determine the displacement field for a single normal fault embedded in sediments are fault height overburden effective stress stiffness and residual friction angle or post peak strength proximity to the free boundary biases the displacement pattern which becomes asymmetric although the measured displacements and numerical predictions are similar the measured magnitude requires pronounced low stiffness of the sediment as well as low post peak shear strength this requirement suggests that sediments hosting contraction driven shear faults most likely have high porosity and high clay fraction and have undergone diagenetic reactions involving significant mineral dissolution the diagenetic evolution of the sediment and its current composition may explain the global scaling relationship between the measured displacement and fault height for polygonal fault systems

glacial isostatic adjustment associated with the barents sea ice sheet a modelling inter comparison the 3d geometrical evolution of the barents sea ice sheet bsis particularly during its late glacial retreat phase remains largely ambiguous due to the paucity of direct marine and terrestrial based evidence constraining its horizontal and vertical extent and chronology one way of validating the numerous bsis reconstructions previously proposed is to collate and apply them under a wide range of earth models and to compare prognostic isostatic output through time with known relative sea level rsl data here we compare six contrasting bsis load scenarios via a spherical earth system model and derive a best fit 2 parameter using rsl data from the four main terrestrial regions within the domain svalbard franz josef land novaya zemlya and northern norway poor 2 values allow two load scenarios to be dismissed leaving four that agree well with rsl observations the remaining four scenarios optimally fit the rsl data when combined with earth models that have an upper mantle viscosity of 0 2 2 1021 pa s while there is less sensitivity to the lithosphere thickness ranging from 71 to 120 km and lower mantle viscosity spanning 1 50 1021 pa s gps observations are also compared with predictions of present day uplift across the barents sea key locations where relative sea level and gps data would prove critical in constraining future ice sheet modelling efforts are also identified

regulation of ice stream flow through subglacial formation of gas hydrates localized subglacial zones of high traction help to regulate ice sheet flow geophysical data from a palaeo ice stream suggest that methane gas accumulation and hydrate formation beneath ice sheets can produce such high traction sticky spots

can polygonal faults help locate deep water reservoirs polygonal faults are compaction related normal faults that develop in very fine grained sedimentary successions despite their ubiquity few studies have highlighted the application of polygonal fault mapping to identifying deep water sandstone reservoirs we use three dimensional seismic and borehole data from the maloy slope offshore norway to demonstrate that the distribution cross sectional geometry and throw characteristics of polygonal faults can be used to locate deep water sandstone reservoirs we identify two tiers of polygonal faults in the cretaceous to lower paleogene succession the lowermost tier is stratigraphically restricted to the lower barremian to lowermost turonian succession and likely formed during the early turonian the uppermost tier spans the entire cretaceous succession and likely formed during the maastrichtian an abrupt decrease in the thickness of the upper tier occurs where a 92 m 302 ft thick sandstone rich slope fan is developed in the upper turonian interval furthermore the lower tips of faults in the upper tier which are defined by anomalously high throw gradients cluster at the top of the sandstone resulting in decoupling of this tier from the underlying lower turonian tier we interpret that faults in the upper tier nucleated above the reservoir across the entire slope and that the slope fan sandstone acted as a mechanical barrier to downward fault propagation resulting in abrupt thinning of the tier at the sandstone pinchout we demonstrate polygonal faults are not simply an academic curiosity mapping of these enigmatic structures can have practical applications for the delineation of a variety of reservoir types in hydrocarbon bearing sedimentary basins worldwide

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

diachronous development of master joints of different orientations in different lithological units within the same forearc basin deposits kyushu japan abstract the geometrical and chronological characteristics of joints and subordinate fractures in the miocene 12 6 ma uchiumigawa group kyushu japan strongly depend on the host lithology in massive sandstone units 11 stations joints are normal to bedding and form two suborthogonal sets a master joint set parallel to the bedding strike and a cross joint set perpendicular to the bedding strike in interbedded sandstone mudstone units 11 stations joints are found only in sandstone layers and have the same characteristics as the joints in the thick sandstone units except that the chronology is opposite in nine stations master joints are perpendicular to the bedding strike and cross joints are parallel to the bedding strike the observed joint pattern is tentatively explained by a diachronous formation of master joints which appeared first in massive sandstone units and later in the interbedded units as a result of the superposition in the study area of two different deformation episodes independently documented by regional fault slip data transition between the two jointing events took place around 6 ma

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

3d polarimetric gpr coherency attributes and full waveform inversion of transmission data for characterizing fractured rock ground penetrating radar gpr can detect and describe fractures to help us characterize fractured rock formations a fracture alters the incident waveform or wave shape of a gpr signal through constructive and destructive interference depending on the aperture fill and orientation of the fracture because the electromagnetic em waves of gpr are vectorial features exhibiting strong directionality can change the state of polarization of the incident field gpr methods that focus on changes in waveform or polarization can improve detection and discrimination of fractures within rock bodies an algorithm based on coherency a seismic attribute that delineates discontinuities in wavelet shape is developed for polarimetric gpr it uses the largest eigenvalue of the time domain scattering matrix when calculating coherence this algorithm is sensitive to wave shape and is unbiased by the polarization of gpr antennas polarimetric coherency works better than scalar coherency in removing the effects of polarization on field data collected from a fractured limestone plot used for hydrologic experimentation another method for time domain full waveform inversion of transmission data quantitatively determines fracture aperture and em properties of fill based on a thin layer model inversion results from field data show consistency with the location of fractures from reflection data these two methods offer better fracture detection capability and quantitative information on fracture aperture dielectric permittivity and electrical conductivity of the fill than traditional gpr imaging and scalar coherency attributes

conduction phenomena from theory to geotechnical practice virtually all geotechnical problems involve the flow of fluids chemicals and energy a current review of the types of direct and coupled flow through soil is given and assessment of their significance in geotechnical practice is made darcy s fourier s ohm s and fick s laws provide a suitable practical basis for the analysis of water heat electrical and chemical flows due to gradients of the same type prolonged application of gradients of the different types can cause significant changes in the state and properties of a soil and flows through it the quantification of coupled flows is most easily done by direct measurement of coupling coefficients when only two types of flow are important the application of irreversible thermodynamics is useful for quantification of flows in more complex systems relationships are provided for the expression of coupling coefficients in terms of directly measurable soil parameters such as hydraulic conductivity coupled fluid flows due to electrical and chemical gr

stagnation of ice stream c west antarctica by water piracy the dynamic behavior of the west antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea level rise attention is focused on the fast moving and rapidly responding ice streams that drain the ice sheet one of these ice stream c largely stopped about a century ago and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice sheet here new data are presented indicating that the slowdown of the ice stream is restricted to its lower part and occurred because of loss of lubrication on localized sticky spots at the bed of the ice stream the increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream b together with slow drawdown of the ice sheet rather than from any general stabilizing feedbacks

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

late cretaceous cenomanian to campanian paleoenvironmental history of the eastern canadian margin of the western interior seaway bonebeds and anoxic events abstract upper cretaceous strata in the pasquia hills of the northern manitoba escarpment eastern saskatchewan canada provide a detailed paleoenvironmental and sea level record of the eastern margin of the western interior seaway sediments deposited during the cenomanian turonian greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column with bottom water anoxia recurrently reaching into the photic zone a middle cenomanian sea level lowstand event followed by transgression left a series of bonebeds within the belle fourche member of the ashville formation indicating a sedimentary environment starved of coarse siliciclastics maximum sea level resulted in the formation of limestone beds within the favel formation further favoured by reduced terrigenous sediment input compared to the western margin limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions and reducing zoo and phytoplankton diversities during final greenhorn regression eastern saskatchewan probably turned into a restricted basin severely limiting marine circulation poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the cenomanian turonian transgressive regressive cycle this was caused either by a freshwater lid stratification of boreal and tethyan derived watermasses or both to various intensities affected by changing sea level basin oxygenation during niobrara time varies between localities along the eastern margin as documented by presence absence of benthic and planktic foraminifera

joint orientation in devonian rocks in the northern portion of the lower peninsula of michigan the orientations of 4 787 joints were measured at 43 separate locations in the area from charlevoix michigan to alpena michigan and north to the tip of the lower peninsula of michigan the sample localities are all in devonian carbonate rocks and shales of the michigan basin nearly all of the joints are vertical at least one major joint set is identifiable at each location and four major sets are present at more than half of the locations at 40 of the 43 sample localities there is a joint set with a strike of about 54 degrees n54 e at 35 locations there is a set striking about 133 degrees n47 w at 32 locations there is a set with a strike of about 92 degrees n88 w and a set with a strike of about 2 degrees no2 e is present at 31 sample localities mean orientation of any of the four joint sets does vary from location to location but is relatively consistent over the entire area for each of the sets fluctuations in mean orientation of any of the joint sets or the presence or absence of the joint sets is independent of formation lithology and distance between sample stations joint set orientation is independent of the regional strike around the michigan basin which varies from 54 degrees n54 e to 114 degrees n66 w within the study area the joint pattern does not appear to be related to structural trends previously postulated to exist in the precambrian basement of the area two of the joint sets may be related to major low amplitude folds in the paleozoic strata of the michigan basin in situ stress measurements show the orientation of maximum horizontal compressive stress to be compatible with these joint sets and the folds

orthogonal fracture systems at the limits of thrusting an example from southwestern wales abstract a well developed orthogonal vein system is located in the autochthonous foreland just beyond the limits of variscan thrusting in southwestern wales the two vein sets trend 200 and 290 perpendicular and parallel respectively to variscan structures the veins contain stretched quartz fibers indicating horizontal extensions of between 0 3 and 2 5 the 200 set has greater extension with a distinctive morphology including shorter more curvilinear fractures that have components of normal offset vein intersections are simple indicating episodic growth by alternating regional propagation of each set during propagation maximum compression was subvertical and the horizontal principal stresses switched direction with the alternation of set growth the system formed during waning variscan compression when the directions of horizontal principal stresses were still controlled by the tectonic compression the differential stress may have been greater during propagation of the 200 set this example indicates that orthogonal fracture systems in forelands beyond thrusting 1 are initiated by fracturing parallel to tectonic compression 2 form in a few stages that are controlled by changes in regional stress and 3 form during waning tectonic compression that controls fracture orientations

conditions of vein formation in the southern appalachian foreland constraints from vein geometries and fluid inclusions abstract the nolichucky shale in the whiteoak mountain thrust sheet of the southern appalachian foreland contains four coeval bed normal calcite vein sets that trended 015 055 090 and 320 before thrusting the pretectonic veins were displaced by syn tectonic bed parallel slickensided calcite veins during local alleghanian thrusting fluid inclusion thermometry indicates precipitation of both bed normal and bed parallel veins from nacl cacl2 brines 27 wt nacl equiv salinity at 80 110 c for bed normal veins and 110 c for bed parallel veins these temperatures correspond to burial depths of 2 4 3 6 km which were attained after the middle mississippian these pressure corrected homogenization temperatures are comparable to time temperature indicators such as cai and illite crystallinity and indicate that inclusions were trapped near maximum burial conditions and were not deformed after trapping this conclusion is supported by the absence of petrographic evidence for inclusion failure and a worst case mechanical analysis that indicates a lack of brittle deformation to inclusions after trapping the four coeval bed normal vein sets could not be formed by one simple stress field nor by the development of a single structure but required the interaction of at least two stress components or structures it is proposed that the interaction of the alleghanian and ouachita orogenic stress components beyond the limits of thrusting produced the sets as coeval alleghanian orthogonal 055 320 and ouchita sub orthogonal 015 090 mode i fractures

late cenozoic environmental changes along the norwegian margin abstract our ability to understand the rates and consequences of contemporary climate change is limited by the insufficient duration of instrumental records thus we are not able to fully understand the processes that provide a fundamental control in driving climate changes across different timescales palaeo climate archives like those preserved offshore norway provide our only real window through which to observe long term rates and styles of climate change this paper reviews the extensive geological and geophysical data available from the late cenozoic atlantic margin of norway along the margin periods of erosion and deposition have been controlled by agents including fluvial glacial and oceanographic processes current controlled sedimentation along the margin provides insight into the connection of the arctic and atlantic oceans from the miocene onward plio pleistocene shelf edge progradation of up to 150 km can be linked to the grounding of ice sheets on the continental shelf through observations of buried grounding zone wedges and mega scale glacial lineations the margin is also important for understanding the ability of glaciation to cause topographic relief changes and generate offshore geohazards such as the storegga slide which mobilised some 3000 km 3 of sediments during the holocene whilst the processes operating along the norwegian margin are well understood through the late cenozoic there is little geochronological control with which to constrain the environmental changes that have been observed concomitant with the wealth of knowledge and the extensive data that are currently available we propose that the norwegian margin is an ideal location to be considered for future ocean drilling the observations of multiple processes acting independently and together means ocean drilling could yield information of global significance due to the bridging location of norway s atlantic margin between the arctic and lower latitudes

episodic basin wide hydrofracturing of overpressured early cenozoic mudrock sequences in the north sea basin a deformational fabric associated with the early cenozoic mudrock dominated sequences of the north sea is described seismic data show that the mudrock sequences are pervasively faulted over a large area of the basin axis in the central and northern north sea mapping the faults using regional two and three dimensional data shows that the faults are minor extensional structures arranged in stratigraphically bound tiers in the deep water sequences and bounded by regional condensed sequences seals the geometry of the faulting is complex faults are organized into cellular networks comprising polygonal prismatic and pyramidal forms a gravitational mechanism of downslope collapse faulting is rejected on the grounds that the distribution of the deformed sequences extends over large areas of formerly horizontal basin plain a mechanism involving the repeated development of basin wide overpressured compartments is proposed in which the cellular structure is related to deformation patterns associated with a density inversion between the overpressured units and the overlying seal hydrofracturing is invoked to account for the almost random strike distribution of the faulting the region affected by the pervasive fluid expulsion faulting encompasses almost half of the north sea basin basin wide collapse of the overpressured compartments could have resulted in a geologically rapid flux of enormous volumes of pore fluids this mechanism has implications for concepts of steady state compaction heat flow in basins hydrocarbon transport and the genesis of lead zinc ore deposits

late cenozoic stress field and fracturing in the iberian chain and ebro basin spain detailed study of mesoscopic faults and joints affecting neogene and pleistocene deposits in the iberian chain and the ebro basin involving statistical study of fracture directions and palaeostress analysis from striated fault planes together with analysis of macrostructures suggest a complex late cenozoic stress field in which both primary and secondary stress systems are superposed 1 regional n s compression was caused by convergence between the iberian and african plates 2 multidirectional extension was caused by crustal doming in the iberian chain 3 stress trajectories were deflected near major faults 4 small scale swapping of the horizontal tension axes 2 and 3 was caused by development of fractures at right angles to either the primary or the deflected 3 axis

fractures in the northern plains stream patterns and the midcontinent stress field fractures in late cretaceous to late pleistocene sediments in saskatchewan eastern montana and western north dakota form two vertical orthogonal sets trending northeast southwest and northwest southeast the pattern is consistent regardless of rock type or age except for concretionary sandstone both sets appear to be extensional in origin and are similar in character to joints in alberta modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures elevation variations on the sub mannville early cretaceous unconformity form a rectilinear pattern also parallel to the fracture sets suggesting that fracturing was initiated at least as early as late jurassic it may have begun earlier but there are insufficient data at present to extend the time of initiation we interpret the fractures as the result of vertical uplift together with plate motion the westward drift of north america the northeast southwest directed maximum principal horizontal