ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

clastic dykes in over consolidated tills evidence for subglacial hydrofracturing at killiney bay eastern ireland abstract a swarm of vertical gravel filled dykes up to 6 m high and several decimetres wide cut through an over consolidated till at killiney bay the dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments burst out structures such features have not previously been described these clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till the burst out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow evidence suggests that the hydrofractures formed subglacially probably during a minor re advance their presence in late devensian 26 13 ka bp tills with an irish sea provenance irish sea till may have important implications for the subglacial hydrology of the last irish sea ice sheet these hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits they greatly affect the geotechnical properties of irish sea tills in particular providing very permeable routes through otherwise impermeable layers with important consequences in situations elsewhere in the irish sea basin where they have been used as aquicludes in landfill and low level nuclear waste disposal sites

groundwater flow beneath ice sheets part ii its impact on glacier tectonic structures and moraine formation abstract meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub surface heads and effective pressures a subglacial groundwater flow model is used together with an ice sheet loading model to compute the magnitudes and directions of the principal effective stresses in the subsurface from which the distribution of different types of sub surface failure in the subglacial and proglacial zones are deduced zones of hydrofracturing shear fracture and pervasive shear failure are distinguished beneath the ice sheet divide area intact rocks of high tensile strength may fail hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward filled and downward filled sediment dykes and till wedges quicksand conditions are developed where strong vertical seepage pressures occur producing sediment diapirism it is suggested that subglacial permeability magnitude may be the product of a self organising process certain types of moraine extrusion moraines are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater it is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines and that many large ancient and modern examples are produced in this setting

effect of commercial trawling on the deep sedimentation in a mediterranean submarine canyon abstract in order to study sediment accumulation rates in the palamos submarine canyon northwestern mediterranean during the last century three sediment cores were extracted from the canyon axis at depths of 450 1200 and 1750 m respectively where instrumented moorings were previously located estimated sedimentation rates based on 210 pb and 137 cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends during the seventies a two fold increase of the sediment accumulation rate took place at the 1750 m depth site this change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies the surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries an activity that may enhance the input of resuspended particles into canyons and eventually trigger sediment gravity flows our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds eventually extending to bathyal depths hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought

mapping of large scale diapir structures at the paleo ice tongue bed in western latvia from geophysical investigations and borehole data abstract this study comprises the investigation of the complex and deformed late pleistocene sedimentary sequence in western latvia composed of sandy sediments that are protruded by large scale clayey silt diapirs and covered by glaciotectonically disturbed discontinuous patches of the late weichselian till we use detailed measurements by ground penetrating radar gpr and electrical resistivity tomography ert combined with borehole data and sedimentological investigations at the baltic sea cliffs to map and characterize the large scale deformation structures and discontinuous till patches we distinguish the intriguing and previously not detected characteristics of the spatial distribution pattern of discontinuous till layer represented as elongated up to 150 m long and up to 50 m wide patches parallel to the seacoast and perpendicular to the latest ice flow direction the upper surface of till patches is flat and not inclined in any direction that is partially explainable by the postglacial erosion of the baltic ice lake the possible locations of diapirs inland are drawn from gpr data we relate the formation of observed large scale deformations to subglacial diapirism induced by the ice loading of the advancing apri i ice tongue clayey silt sediments become loaded and overpressurized and flowed upwards intruding into the overlying sandy sediments the initial deposition and deformation of till layer could have been affected by the diapirism process and preferred accretion of till in inter diapir spaces we demonstrate that the geophysical methods can greatly supplement traditional geological investigations in the field revealing characteristics of deformed sediment sequences that are not recognizable from the outcrop data only and thus can have significant implications on the interpretation of deformation processes

the use of integrated sedimentological and geophysical methods in drumlin research a case study of pigeon point clew bay northwest ireland despite significant advances over the past decades our understanding of drumlin formation and associated ice bed processes is still incomplete in this paper we present the integrated use of geomorphological sedimentological and geophysical techniques as a powerful means to force a breakthrough towards solving the drumlin enigma we report on investigations of the anatomy of the pigeon point drumlin clew bay ireland we found that the bulk of the landform which displays a classical drumlin shape consists of silty clayey diamicton showing evidence of deformation hydrofracturing and comminution the unit is interpreted as a sub glacial traction till comminution till the thin unit overlying this basal till consists of silty sandy diamicton and is interpreted as a para glacially modified melt out till the partly cemented third unit consists of stratified massive to graded sands and gravels its contact with the sub glacial traction till consists of a series of concave shapes which suggests that it was deposited in meltwater channels that flowed in sub glacial cavities and that cut laterally into the drumlin we propose that highs in the undulating rockhead relief as shown in the seismic profile have provided nuclei which initiated drumlin formation this idea is supported by the observation of local detached bedrock slabs that grade upwards into a comminution till in the long profile very high normalized induced polarization ip values form a wedge shape which is interpreted as a set of conjugate thrusts or a pop up structure the structure is positioned directly above one of the undulations in the bedrock suggesting a direct relationship the high values are thought to reflect the presence of pre existing clays which were sheared into the till thus forming linings in the thrust features it is concluded that glacitectonic processes notably differential bedrock weathering and thrusting have played a key role in the formation of this drumlin

trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon abstract commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution in particular trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves but the issue is at present poorly documented with direct observations this paper analyses changes in water turbidity in a tributary valley of the la fonera palamos submarine canyon whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m a string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years 2010 2011 the second year an adcp profiled the currents 80 m above the seafloor the results illustrate that near bottom water turbidity at the study site is heavily dominated both in its magnitude and temporal patterns by trawling induced sediment resuspension at the fishing ground resuspended sediments are channelised along the tributary in the form of sediment gravity flows being recorded only during working days and working hours of the trawling fleet these sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom reaching suspended sediment concentrations up to 236 mg l 1 close to the seafloor 5 m above bottom a few hours after the end of daily trawling activities water turbidity progressively decreases but resuspended particles remain in suspension for several hours developing bottom and intermediate nepheloid layers that reach background levels 2 mg l 1 before trawling activities resume the presence of these nepheloid layers was recorded in a ctd turbidimeter transect conducted across the fishing ground a few hours after the end of a working day these results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development

increasing sediment accumulation rates in la fonera palamos submarine canyon axis and their relationship with bottom trawling activities previous studies conducted in la fonera palamos submarine canyon nw mediterranean found that trawling activities along the canyon flanks cause resuspension and transport of sediments toward the canyon axis 210pb chronology supported by 137cs dating applied to a sediment core collected at 1750 m in 2002 suggested a doubling of the sediment accumulation rate since the 1970s coincident with the rapid industrialization of the local trawling fleet the same canyon area has been revisited a decade later and new data are consistent with a sedimentary regime shift during the 1970s and also suggest that the accumulation rate during the last decade could be greater than expected approaching 2 4 cm yr 1 compared to 0 25 cm yr 1 pre 1970s these results support the hypothesis that commercial bottom trawling can substantially affect sediment dynamics and budgets on continental margins eventually initiating the formation of anthropogenic depocenters in submarine canyon environments

bottom trawling contribution to the spatio temporal variability of sediment fluxes on the continental shelf of the bay of biscay france abstract based on experiments a trawling induced erosion dynamics was included in a 3d realistic and pre validated hydro sedimentary model so as to assess its contribution to the overall regional sediment dynamics in the specific case of the bay of biscay continental shelf the effect of trawling was investigated throughout a 5 year period in terms of horizontal vertical fluxes and changes in seabed mud content and compared to the natural variability of sediment fluxes at different spatio temporal scales trawling is shown in the model to significantly contribute to sediment re suspension and changes in the seabed at the scale of the shelf the contribution of trawling to re suspension is 80 during the high fishing season at many locations on the outer shelf and over the grande vasiere area a large and intensively trawled muddy zone located in the middle of the shelf the contribution of trawling is significantly weaker in winter and at annual scale particularly over zones with muddy sand facies between 1 and 1 but remains high and reaches 20 of the annual erosion over muddy areas e g northern part of the grande vasiere this significant trawling induced erosion dynamics results in high sediment fluxes which increase natural poleward dynamics from a few percent up to 40 and contributes to the natural offshore export of sediment on the outer shelf e g 35 of mud fluxes along the 130 m isobath it is noteworthy that trawling induced fluxes are larger in winter although the corresponding re suspension is lower than in summer this is due to stronger near bottom flows occurring at this period largely influenced by energetic wind conditions in contrast on the inner shelf trawling induced sediment fluxes are rather oriented towards the coast finally simulation results reveal a trawling signature on changes in the seabed a significant decrease between 10 and 50 in mud content is simulated over trawling hotspots especially over the internal part of the grande vasiere and on mud patches located in front of the gironde estuary conversely trawling causes or intensifies mud deposition on both sides of these preferentially trawled areas

entrainment of glaciomarine sediments and formation of thrust block moraines at the margin of sorsdale glacier east antarctica the morphology sedimentology and structure of moraines at the margin of an outlet glacier in east antarctica are described and contemporary depositional processes in a marine inlet adjacent to the ice margin are examined results indicate that the principal moraines are thrust block moraines produced by basal freezing and deformation of glaciomarine sediment as the outlet glacier expands into a marine inlet preservation of detailed glaciomarine sedimentary structures and beds of marine shells suggests that the sediment was frozen during entrainment transportation and deposition the presence of low angle faults in the moraines show that the moraines consist of an en echelon arrangement of thrust plates the sedimentology structure thickness of the thrust plates and inferred entrainment processes are consistent with weertman s ice debris accretion hypothesis for debris entrainment at the edge of cold ice sheets a model of thrust block moraine development produced by this study provides a framework for the interpretation of radiocarbon dates from marine macrofossils in the moraines the model may also be useful in the interpretation of similar moraines in coastal east antarctic oases and other polar marginal marine environments 1997 by john wiley sons ltd

micromorphological evidence of liquefaction injection and sediment deposition during basal sliding of glaciers the sliding of an ice mass over its bed represents one of the main mechanisms for the forward motion of glaciers and ice sheets facilitated by the periodic introduction of meltwater along the ice bed interface or regelation of the overriding ice in the geological record however physical evidence of this process having occurred beneath former ice masses is apparently limited this paper presents the results of a detailed micromorphological study of thinly stratified subglacial tills exposed at two sites i galmis in switzerland and ii plumpe farm near gretna in sw scotland the stratification within these tills comprises alternating layers of massive to weakly foliated diamicton and variably deformed folded faulted laminated silt and clay microtextural and microstructural evidence is interpreted in terms of repeated phases of basal sliding as the ice overrode a soft sediment bed elevated meltwater contents pressures encountered immediately prior to and during basal sliding promoted localised liquefaction within the bed decoupling of the ice mass from its bed enabled the injection of the liquefied diamicton along the ice bed interface and or into the laminated sediments immediately adjacent to this boundary the laminated silts and clays record the settling out of fines clay silt from meltwater trapped along the ice bed interface after an individual phase of basal sliding has ceased injection of till into the locally water saturated silts and clays resulted in partial liquefaction and incomplete mixing of these fine grained sediments with the diamicton density contrasts between the two liquefied sediments led to the development of a complex vinaigrette like texture comprising rounded to irregular till pebbles within a matrix of variably homogenised silty clay recoupling of the ice with its bed led to localised folding and thrusting within the laminated silts and clays hydrofracturing and injection of a network of sand filled veins and the imposition of a variably developed clast microfabric in the diamicton layers analysis of the clast microfabrics indicates that the intensity of these fabrics is highly variable reflecting the variation in the intensity of deformation imposed by the overriding ice

diapiric deformations in the quaternary deposits of the central ebro basin spain from a study of 24 outcrops in neogene and quaternary deposits of the central ebro basin a number of diapiric deformations have been recognized two principal types being differentiated domal or pillow structures and piercement or intrusive structures the former are incipient diapirs of gypsum piercing structures have reverse faulted contacts not caused by halokinesis here neogene marls are the active plastic material contrasting with the competent behaviour of gypsum these intrusive structures are viscous diapirs which easily pierce the non consolidated low strength quaternary gravel overburden and submit it to a horizontal compressive stress as a consequence reverse faults and flexures develop in it generally normal faults and tension cracks do not appear underlying gypsum beds are frequently pulled up into diapirs and they constitute the structural core density contrast and conditions for plastic flow exist at the marl gravel boundary it seems to have been specially common at the time of quaternary fluvial sedimentation so that much deformation is synsedimentary diapiric phenomena have been very active during early to middle pleistocene time becoming weaker afterwards

numerical modeling of bottom trawling induced sediment transport and accumulation in la fonera submarine canyon northwestern mediterranean sea bottom trawling leads to recurrent sediment resuspension events over fishing grounds recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons which subsequently impacts deep sea ecosystems present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed the present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in la fonera submarine canyon northwestern mediterranean sea thus contributing to an improved assessment of trawling impacts based on mooring data within a canyon gully we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds this resuspension is later used as forcing for the direct problem we simulate trawling induced flows through the canyon and provide a 3d visualization of potential trawling impacts on sediment dynamics including the identification of the propagation patterns of sediments resuspended by trawling flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope trawling induced sediment flows promote sediment accumulation beyond the canyon mouth given the wide geographical distribution of bottom trawling our results have far reaching implications that go much beyond la fonera submarine canyon our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins

flow speed estimated by inverse modeling of sandy sediment deposited by the 29 september 2009 tsunami near satitoa east upolu samoa abstract sandy deposits from the 29 september 2009 tsunami on the east coast of upolu samoa were investigated to document their characteristics and used to apply an inverse sediment transport model to estimate tsunami flow speed sandy deposits 6 to 15 cm thick formed from 25 to 250 m inland sedimentary layers in the deposits that are defined by vertical grain size variation and contacts are interpreted to have formed during onshore runup of two waves deposits at 3 locations 100 170 and 240 m inland contained two layers that are predominately normally graded 80 but contained massive sections 15 and inversely graded sections 5 at their bases about 75 of the total thickness of normally graded intervals exhibits a signature of sediment falling out of suspension at their top this type of grading termed suspension grading here was first recognized in turbidity current deposits and is characterized by the entire distribution shifting finer upwards in a layer as high settling velocity coarser material deposits first and low settling velocity finer material deposits last the jaffe and gelfenbaum 2007 inverse sediment transport model was applied to intervals within layers that exhibited suspension grading to estimate tsunami flow speed and was able to reproduce the general trends of the observed suspension grading a key unknown input in the modeling is the bottom roughness for a bottom roughness parameterization using a manning s n of 0 03 equivalent to a z0 0 006 m for the observed flow depths of 2 3 m flow speeds calculated for the 2 layers at the 3 locations were 3 8 3 6 and 3 7 m s bottom layer earlier wave and 4 4 4 4 and 4 1 m s top layer later wave at 100 170 and 240 m inland respectively these estimates are consistent with the 3 8 m s tsunami flow speed from boulder transport calculations and result in froude numbers of 0 7 1 0 when maximum measured flow depths are used because the inverse model assumes the deposit was formed by sediment falling out of suspension care must be taken to model only intervals of the deposit exhibiting suspension grading including intervals deposited by either bedload or suspended load transport convergences result in higher and sometimes unrealistic tsunami flow speed estimates

origin of elblag upland northern poland and glaciotectonism in the southern baltic region abstract elblag upland is a complex glaciotectonic landform located near gdansk bay in northern poland we conducted surface subsurface and remote sensing investigations to elaborate the internal structure and morphology of the upland the upland covers some 390 km 2 and rises more than 150 m elbl g upland consists almost entirely of pleistocene strata many of which are strongly deformed anomalously thick and situated high above their normal levels these deformed sediments were derived from source basins located to the northeast and possibly west of the upland elbl g upland was created by north polish vistulian weichselian ice advances which pushed locally from the northeast and possibly the west the upland was then overridden by ice coming from the north northwest we propose that glaciotectonic deformation occurred as a result of ice lobe advances possibly surges over unconsolidated and unfrozen sediments in which high pore water pressures existed in confined aquifers surges may have been either local or regional in character and surging may have taken place repeatedly during vistulian glaciation glaciotectonism played a prominent role in shaping the southern baltic basin which represents a geomorphic end product of multiple pleistocene glaciations

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

palynology and lithostratigraphy of late elsterian to early saalian aquatic sediments in the ziemupe jūrkalne area western latvia abstract this study is based upon lithological and palynological investigation of test drilling cores along the baltic sea coast three intertill units of basin sediments are underlain by a thin layer of l ti a elsterian till and overlain by glaciotectonically deformed kurzeme saalian complex till the kurzeme till differs from the l ti a till by higher contents of limestone clasts and rounded hornblende grains the lowermost intertill unit consists of glaciolacustrine to glaciomarine laminated clay of the sudrabi member a late glacial deposit of the l ti a glaciation treeless vegetation covered the adjoining land next is the marine to brackish akme n rags formation deposited during the pulvernieki holstenian interglaciation thermophilous deciduous trees spruce and alder dominated the forests during its climatic optimum the youngest dominantly sandy j rkalne formation was deposited in brackish to freshwater at the beginning of the kurzeme saalian complex glaciation when land was covered by treeless vegetation it contains a thin interbed of diamicton of kurzeme till lithology suggesting a brief glacial advance in the baltic sea basin at the beginning of the kurzeme glaciation

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

understanding sediment dynamics of two large submarine valleys from seafloor data blanes and la fonera canyons northwestern mediterranean sea abstract the studied area appears as a major place for dense shelf water dsw formation and export towards the deep basin with blanes and la fonera canyons as most efficient pathways these two canyons are so deeply indented on the continental shelf and slope of the northern catalan margin western mediterranean sea that their heads significantly reduce the width of the shelf and interfere with coast and contour parallel sediment transport patterns this study presents the results of the analysis of swath bathymetry data and parametric seismic reflection profiles showing the detailed morphology and uppermost sedimentary structure of blanes and la fonera canyons with the focus on their heads and adjacent upper courses and shelf the main aim is to understand their functioning and assess how they influence and respond to the hydrosedimentary processes active in the study area the n s oriented blanes canyon head whose shortest distance to shore is only 4 km extends along 21 7 km from 70 to 1300 m water depth with an average rim to rim width of 8 km and a canyon floor width up to 750 m la fonera canyon head extends along 28 km from 60 to 1700 m water depth rim to rim and canyon floor widths are up to 7 km and up to 700 m respectively the canyon head follows a general wnw ese trending course in its deeper part but trends n s in its shallower course formed by cap begur branch south of it the illa negra branch trends nw se and its tip located at 60 m water depth and 800 m from the coastline intersects the littoral sedimentary prism backscatter data show high reflectivity into both blanes and la fonera canyon floors as well as on tributary gullies which at these locations is indicative of coarse sediment the seafloor and subseafloor observations here presented are explained and best understood from the sedimentological viewpoint by the interplay of event driven dsw flows permanent mesoscale circulation and storm action while dsw flows from the gulf of lion and the shelf area around the studied canyons are the most dynamic agent in terms of sediment transport and seafloor shaping the northern current ensures background sedimentation of fines and coastal storms promote episodic entries through canyon heads and upper course rims canyon wall morphology and sediment draping respond to the currentward or leeward position of each wall with respect to the main southward moving water flows in the area either episodic or permanent that are dsw and the northern current other relevant morphosedimentary features such as a 40 km long southbound subdued channel on the roses outer shelf that originates off cap de creus promontory to finally feed cap begur branch of la fonera canyon and a contouritic ridge and moat attached to the northern wall of the canyon are interpreted in terms of dsw flows a comprehensive model of the sedimentary functioning of the canyoned north catalan margin that integrates seafloor information and background data on dynamic processes is presented which could be of application to other continental margins worldwide such an integrative view is eased by the enormous unprecedented multidisciplinary research effort carried out in the study area over the last three decades

the impact of shrimp trawling and associated sediment resuspension in mud dominated shallow estuaries abstract to address the relative importance of shrimp trawling on seabed resuspension and bottom characteristics in shallow estuaries a series of disturbance and monitoring experiments were conducted at a bay bottom mud site 2 5 m depth in galveston bay texas in july 1998 and may 1999 based on pre and post trawl sediment profiles of 7be pore water dissolved oxygen and sulfide concentration and bulk sediment properties it was estimated that the trawl rig including the net trawl doors and tickler chain excavate the seabed to a maximum depth of approximately 1 5 cm with most areas displaying considerably less disturbance water column profile data in the turbid plume left by the trawl in these underconsolidated muds 85 90 porosity

a complex subglacial clastic dyke swarm solheimajokull southern iceland abstract a complex network of clastic dykes dissects loosely consolidated holocene sediments along the east flank of the proglacial braid plain of solheimajokull southern iceland the dykes comprise downward bifurcating intrusions up to 0 5 m thick and several metres in length and are intruded into glaciogenic deposits sandy gravel gravelly sand interlaminated silt and sand and diamicton the dykes were sourced from a clast poor sandy diamicton interpreted as a subglacial till and were intruded downwards beneath solheimajokull glacier during a previous phase of advance as the glacier advanced southwards it loaded the sediment column resulting in the intrusion of dykes with a consistent south southwest dip with rare northward dipping examples the dyke fills are characterised by laminated sediment with laminae oriented parallel to the dyke margins and comprise interlaminated clay silty clay silt sand sandy gravel and diamicton in some dykes high concentrations of pebble to boulder sized clasts occur in association with rotated pods of the laminated sediment the laminae are thought to have evolved by a slow long lived intrusion process that involved the repeated fracture and expansion of the host sediments followed by viscous smearing on of subglacial material onto the dyke walls rather than rapid injection of fluidised sediment

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

general patterns of circulation sediment fluxes and ecology of the palamos la fonera submarine canyon northwestern mediterranean abstract currents particle fluxes and ecology were studied in the palamos submarine canyon also known as the fonera canyon located in the northwestern mediterranean seven mooring arrays equipped with current meters and sediment traps were deployed along the main canyon axis on the canyon walls and on the adjacent slope additionally local and regional hydrographic cruises were carried out current data showed that mean near surface and mid depth currents were oriented along the mean flow direction ne sw although at 400 and 1200 m depth within the canyon current reversals were significant indicating a more closed circulation inside the canyon mean near bottom currents were constrained by the local bathymetry especially at the canyon head the most significant frequency at all levels was the inertial frequency a second frequency of about three days attributed to a topographic wave was observed at all depths suggesting that this wave was probably not trapped near the bottom the current field observed during the most complete survey revealed a meandering pattern with cyclonic vorticity just upstream from and within the canyon the associated vertical velocity ranged between 10 and 20 m day and was constrained to the upper 300 m this latter feature together with other computations suggests that during this survey the meander was not induced by the canyon but by some kind of instability of the mean flow in the canyon suspended sediment concentration downward particle fluxes chlorophyll and particulate c and n were significantly higher up canyon from about 1200 m depth than offshore defining along with the different hydrodynamics two canyon domains one from the canyon head to about 1200 m depth more affected by the canyon confinement and the other deeper than 1200 m depth more controlled by the mean flow and the shelf slope front the higher near bottom downward total mass fluxes were recorded in the canyon axis at 1200 m depth along with sharp turbidity increases and are related to sediment gravity flows during the deployment period the increase in downward particle fluxes occurred by mid november when a severe storm took place on the canyon walls at 1200 m depth suspended sediment concentrations downward particle fluxes chlorophyll and particulate c and n were higher on the southern wall than on the northern wall inversely to the current s energy this could be caused by an upward water supply on the southern canyon wall and or the mean flow interacting with the canyon bathymetry in the swimmers collected by the sediment traps the dominant species was an elasipod holothurian which has not been recorded in other canyons or elsewhere in the mediterranean indicating particular speciation

density driven deformation structures in glacigenic consolidated diamicts examples from traeth y mwnt cardiganshire wales u k abstract density driven deformation may occur when a sediment of higher bulk wet density is deposited on top of one of a lower bulk wet density and occurs commonly in glacigenic sediments by recognizing density driven deformation of gravels and sands embedded in diamicts it is possible to reconstruct relative preconsolidation states of the diamicts density driven structures indicate that during deformation the diamict behaved as a viscous fluid thus providing important evidence for the viscosity and physical state of diamicts after deposition which has implications for the depositional environment the density driven process and its implications for reconstructing depositional environments is discussed criteria are given for the recognition of density driven deformation stages of gravels and sands deposited on top of a viscous mud

analysis of factors determining sediment yield variability in the highlands of northern ethiopia in many developing countries sustainable land management and water resources development are threatened by soil erosion and sediment related problems in response to such threats there is an urgent need for improved catchment based erosion control and sediment management strategies the design and implementation of such strategies require data on erosion rates and understanding of the factors that control the delivery of sediment through the catchment system in this study reservoir sedimentation and corresponding catchment attribute data were used to investigate the major factors controlling sediment yield variability in a mountainous dryland region of northern ethiopia sediment yield data were acquired for representative 11 catchments above reservoirs geomorphological and anthropogenic catchment attributes were extracted for each reservoir from different sources including digital elevation models satellite images and field surveys different statistical analyses such as pearson s correlation principal components and multiple regression were implemented to analyze the relationship between sediment yield and catchment characteristics and to determine the major factors controlling the variability of sediment yield the results show that terrain form gully erosion surface lithology and land cover explain most of the variability in sediment yield among the catchments the implications of the results for relevant management intervention targeted at ameliorating the major causative factors of erosion are also outlined

spatial distribution of sedimentation rate increases in blanes canyon caused by technification of bottom trawling fleet abstract a detailed study of 15 sediment cores from blanes canyon and its immediate surroundings nw mediterranean sea was conducted to compare historic sedimentation rates and evaluate the possible impact of bottom trawling intensification on the sedimentary regimes over the past 50 years the canyon axis and flanks as well as the adjacent open slope were sampled at water depths ranging from 300 m to 2200 m grain size dry bulk density and 210pb concentration profiles were measured to assess possible changes in sedimentation rates over the last century and their temporal and spatial relationship to bottom trawling effort sedimentation rates in the upper canyon axis 900 1200 m had the highest rates of 0 9 2 1 cm yr 1 quantified since the 1970s farther downcanyon sedimentation rates increased two to five times after the 1970s from 0 1 0 2 cm yr 1 to 0 2 0 8 cm yr 1 which coincides with a rapid growth of the total engine power of the fishing fleet operating in the study area the enhanced sedimentation rates occur downslope of the main fishing grounds and decrease downcanyon as the distance from trawling grounds increases these results highlight the ability of bottom trawling to resuspend bottom sediments leading to net erosion of the canyon rims and flanks in turn large volumes of sediment are advected towards the canyon s interior ultimately increasing sediment deposition along the canyon axis natural sedimentation rates at similar along canyon distance from shore in the untrawled continental slope 900 1500 m and in the lower canyon axis 1500 2200 m are comparable 0 08 0 20 cm yr 1 suggesting distance from coastal sediment sources as the main control on regional sedimentation in deeper parts of the margin while submarine canyons have been regarded as preferential cross margin conduits for sediment dispersal they can also potentially function as modern depocenters for trawling induced sedimentation

osl dating of middle weichselian age shallow basin sediments in western latvia eastern baltic abstract this paper presents the results of the first attempt to date the quaternary sediments of western latvia in the southeast baltic region using luminescence the analyses have been carried out on sandy sediments of the jurkalne formation that are located between upper and lower scandinavian sourced tills previous publications on the origin of the quaternary sediments in the region are reviewed and it is found that there are a wide range of explanations for their processes of formation and their age of formation it is concluded that although the sandy sediments were deposited in freshwater environment although they contain both marine and freshwater fauna and flora a property that is explained by derivation and glaciotectonic deformation and mixing the samples used for dating were collected from surface exposures and boreholes and yield results that range in age from 52 10 ka bp to 26 4 1 ka bp as a result of this study it is suggested that the dated sediments were deposited in a freshwater basin during mis 3 and are overlain by a till deposited by scandinavian ice during the late weichselian mis 2 lgm the underlying till is attributed to a middle weichselian glaciation and tentative suggestions are presented for the age of other deposits that underlie the dated sediment

a simple model for calculating tsunami flow speed from tsunami deposits abstract this paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit the inverse problem for sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport tsunami sediment transport is modeled as a steady spatially uniform process the amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period slowing varying uprush portion of the tsunami spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation there is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness the model is tested using field data collected at arop papua new guinea soon after the 1998 tsunami speed estimates of 14 m s at 200 m inland from the shoreline compare favorably with those from a 1 d inundation model and from application of bernoulli s principle to water levels on buildings left standing after the tsunami as evidence that the model is applicable to some sandy tsunami deposits the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami

deformation styles as a key for interpreting glacial depositional environments lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation we propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation five styles are recognised pure shear p simple shear s compressional c vertical v and undeformed u these dictate the first letter of the codes the remaining letters conveying the evidence this information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed individual structures are not diagnostic of particular environments but the suite of structures their relative scale stratigraphical relationships and orientation relative to palaeoslopes and to palaeoice flow directions can be used to infer the environment in which they formed this scheme is applied at five sites in west wales the typical succession is interpreted as subglacial sediments overlain by meltout tills flow tills and sediment flows paraglacial redistribution of glacial sediments is widespread large scale compressional deformation is restricted to sites where glaciers readvanced large scale vertical deformation occurs where water was locally ponded near the ice margin there is no evidence for glaciomarine conditions copyright 2003 john wiley sons ltd

fine particle retention and deposition in regions of cyclonic tidal current rotation abstract benthic sediments in continental shelf seas control a variety of biogeochemical processes yet their composition especially that of fine sediment remains difficult to predict mechanisms for mud or fine sediment deposition and retention are not fully understood using sediment data and a hydrodynamic model of the northwest european shelf seas a relationship is shown to exist between fine benthic sediment composition and regions of cyclonic tidal current rotation the reduced thickness of cyclonic tidal benthic boundary layers compared with the anticyclonic case promotes deposition of fine sediment and trapping of resuspended material adding the effects of the benthic boundary layer thickness as influenced by ellipticity or not sheds some light on the limitations of approaches only focusing on bed shear stress and sediment pathways to predict the location of mud deposits a tidal boundary layer predictor that includes ellipticity alongside tidal current magnitude and depth was shown to spatially agree with maps of mud deposits

the 1890 surge end moraine at eyjabakkajokull iceland a re assessment of a classic glaciotectonic locality abstract the glaciotectonic architecture and sequential evolution of the eyjabakkajokull 1890 surge end moraines in iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics based on morphological geological and geophysical data from terrain cross profiles cross sections and ground penetrating radar profiles we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the eyjabakkajokull moraines firstly a narrow single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport secondly large lobate end moraine ridges with multiple closely spaced narrow asymmetric crests formed by proglacial piggy back thrusting thirdly a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum this is true for the eastern and western parts of the eyjabakkajokull moraines as they show similar morphological and structural styles which developed to different degrees the former represents an intermediate member with decollement at 4 5 m depth and 27 33 shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface the latter represents an end member with decollement at about 27 m depth and 39 horizontal shortening through multiple high amplitude overturned and overthrusted anticlines appearing as broadly spaced symmetric crests we propose that the opposite end member would be a moraine of multiple symmetric wide open anticlinal crests of low amplitude our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70 190 m of its terminal position this indicates a time frame of 2 6 days for the formation of the end moraines

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

hydrodynamics of turbid underflows i formulation and numerical analysis a mathematical model is developed for unsteady two dimensional single layer depth averaged turbid underflows driven by nonuniform noncohesive sediment the numerical solution is obtained by a high resolution total variation diminishing finite volume numerical model which is known to capture sharp fronts accurately the monotone upstream scheme for conservation laws is used in conjunction with predictor corrector time stepping to provide a second order accurate solution flux limiting is implemented to prevent the development of spurious oscillations near discontinuities the model also possesses the capability to track the evolution and development of an erodible bed due to sediment entrainment and deposition this is accomplished by solving a bed sediment conservation equation at each time step independent of the hydrodynamic equations with a predictor corrector method the model is verified by comparison to experimental data for currents driven by uniform and nonuniform sediment

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

polydiapirs multiwavelength gravity structures polydiapirs domes in domes result from the evolution of a multiwavelength rayleigh taylor gravitational instability the present work investigates the initiation and development of polydiapirs by means of two dimensional finite difference models of gravitationally unstable triple layered sequences of newtonian fluids the values of viscosities thicknesses and densities were systematically varied for selected examples in triple layered sequences only two types of density stratification are likely to result in multiwavelength instabilities that will eventually develop into polydiapiric structures the limiting factors and evolution of such structures were studied for both these types of density stratifications finite difference calculations on models with physical parameters appropriate to evaporitic sequences and covered by a viscous clastic overburden showed that a very small downward density decrease in the evaporitic source may cause an internal overturn that will compete with the main overturn between source and overburden this may lead to the development of sequential or simultaneous polydiapirs the mature polydiapirs in the models exhibit spines curtain folds pendant repetitions of the source layers inside the large diapirs and anomalous interdiapiric distances all these features are known in natural salt diapirs suggesting that polydiapirs may be far more common in nature than hitherto recognized