alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

ploughing boulders along shorelines with particular reference to the st lawrence estuary abstract ploughing boulders are defined as large stones moved by drift ice with a ploughing action into the substrate leaving a linear depression on the back and building a frontal push ridge they are commonly found on unconsolidated tidal flats and on rock shore platforms along cold region shorelines in the marine lacustrine and fluvial environments it is an erosional process of great significance particularly for consolidated substrates a total of 176 ploughing boulders were measured in eighteen localities along the st lawrence estuary the largest boulder weighed 176 tons and was moved 3 m while a 50 t boulder was moved 40 m on shore platforms cut in shales one boulder 49 t has scoured a depression 19 m long and up to 40 cm deep and built a frontal ridge 40 cm high along the st lawrence estuary about 95 of ploughing boulders were moved seaward by ice floes entrained by ebb currents

late ordovician glacial pavements revisited a reappraisal of the origin of striated surfaces late ordovician glacial pavements revisited

case study of a relict iceberg scour exposed at scarborough bluffs toronto ontario implications for pipeline engineering ice scour is a common process on high latitude shelves and has been studied extensively though laboratory and numerical modelling direct observations of ice scours in outcrop are very rare this paper describes a late pleistocene iceberg scour observable in soil cliff exposures at cudia park scarborough bluffs toronto ontario the structure is cut into a glaciolacustrine clayey silt is about 10 m wide and 4 m deep and is filled with sands deposited in shallow water a description of the scour and a simplified finite element model of sub ice scour soil deformation are presented it is estimated that the cudia scour was caused by a small iceberg with a mass of 0 04 mt in a water depth between 10 and 30 m acting with a downward force of 5 mn which is consistent with modern iceberg scours the relevance of the cudia scour to pipeline engineering design burial depths is demonstrated with reference to the design methodology of the centre for cold ocean research and engineering c core the cudia sc

a combination of electrical resistivity seismic refraction and gravity measurements for groundwater exploration in sudan in the savannah belt of central sudan near the town of kosti a regional geophysical survey has been carried out forming part of a groundwater project because of the presence of detectable and significant contrasts in physical properties of the subsoil integrated use could be made of electrical resistivity seismic refraction and gravity methods in the interpretation of multilayer electrical sounding curves additional subsurface information such as lithological well descriptions and geophysical well logs is normally a necessity for solving the problems of equivalence along a profile in the eastern part of the area studied where additional subsurface information was scarce 16 vertical electrical soundings have been made a preliminary simple mathematical interpretation suggested possibilities for the presence of fresh groundwater in the eastern part of the profile in order to solve the equivalence problem seismic refraction work was carried out at some selected places that yielded additional in

a modified seismic reflection approach for engineering geology investigation in fractured rock zones abstract delineating soil rock interface is critical for geotechnical and tunnel site investigations in engineering geology in singapore we also need to draw attention to local faults and fractured rock zones because the regional geology of peninsular malaysia and singapore contains some minor steep and brittle faults propagating at some areas in the island city in addition to drilling boreholes seismic reflection survey is a viable option to mitigate the uncertainties in areas without boreholes however the current practice of seismic reflection still follows the methods used in the petroleum exploration community this investigation reviews and modifies the seismic reflection approach specifically customized for geotechnical and tunnel site investigation which is partly different from petroleum exploration we demonstrate the modified approach through a field testing in singapore the resultant image from the field test fairly captures the soil rock interface and it is validated based on the vertically drilled boreholes a local fault or a fracture rock zone is also identified in the migrated image the extent and location match with the record of horizontal directional coring hdc this addresses the concern of fracture rock zone raised from the regional and local geology and provides useful information for geotechnical and tunnel engineers in addition we further discuss the general challenges of using the modified seismic reflection approach this work aims to help the geotechnical and tunnel community better understand the non invasive seismic reflection survey

micromorphology of iceberg scour in clays glacial lake agassiz manitoba canada abstract icebergs plough through unconsolidated lake sea sediments gouging out kilometre long grooves 100s of metres wide and tens of metres deep although the surface morphology of iceberg scours is well documented little is known about what scours look like in stratigraphic section particularly where surface characteristics are absent e g through decay or burial this investigation establishes a definitive suite of diagnostic criteria for identifying iceberg scours in clays by macroscopically and microscopically 2d thin sections examining sediment deformation below iceberg scours in former glacial lake agassiz manitoba canada structures unequivocally attributed to iceberg scour in this investigation include sub horizontal microfabrics folds sheath folds augen shapes normal faults reverse thrust faults discrete shears partially destroyed clasts intraclasts type iii multiple domains water escape structures flow structures unistrial plasmic fabric dropstones realigned bedding and specific structural sequences this research will be particularly valuable in palaeoenvironmental reconstruction and in predicting glacial dynamics in addition it may eventually aid structural engineering on polar shelves which could be of great value to oil and gas companies

an estimate of ice drifted sediments based on the mud content of the ice cover at montmagny middle st lawrence estuary abstract recent measurements made at montmagny a locality on the south shore of the middle st lawrence estuary 70 km northeast of quebec city 47 n give an idea of the volume of fine grained sediments incorporated in the ice cover and allow an estimation of the annual load drifted by ice at this locality a mean thickness of 10 cm of mud was encountered in the ice cover over an area of approximately 20 km 2 thus the total load of fines may be as much as 4 10 6 tonnes t it is estimated that upon melting at break up about 15 of this load returns to the montmagny tidal flat while the remaining volume is carried to the offshore zone considering breakup characteristics it is estimated that about 1 5 2 10 6 t of fines return to the turbidity zone while the remaining load is ice drifted outside that zone since the shore area of the middle st lawrence estuary covered by ice during the winter is approximately 60 km 2 it is calculated that a load of 5 6 10 6 t of sediment incorporated in the ice cover could escape from the turbidity zone annually to this load should be added another 4 10 6 t of suspended matter which come from the freezing in situ of the turbid water in the offshore zone an annual output by ice drifting of 10 10 6 t of sediment is thus likely and is in great contrast to the output during the ice free season of approximately 1 10 6 t in the middle st lawrence estuary the annual output almost equals the input consequently the sediment budget is virtually in a state of equilibrium which helps to explain why there is very little permanent mud deposition in the shore and offshore zones today it is concluded that ice processes largely control the sedimentary budget of the turbidity zone of the middle st lawrence estuary a particular environment within a mid latitude inner continental shelf which is partly dominated by ice

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

ice melt collapse pits and associated features in the 1991 lahar deposits of volcan hudson chile criteria to distinguish eruption induced glacier melt in subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano s history of lahar generation by glacier melt at volcan hudson in chile catastrophic lahars were initiated by eruption induced melting of glacier ice in august and october 1991 they transported large ice blocks 50 km down the rio de los huemules valley to the sea large current crescents with lee side lenses were formed where ice blocks were deposited during waning stages of the flood when stranded blocks of ice melted they left cone shaped and ring shaped heaps of ice rafted debris on the sediment surface several hundred ice blocks were completely buried within the aggrading lahar sediment and when these melted circular collapse pits formed in the sediment collapse types included subsided coherent blocks of sediment bounded by an outward dipping ring fracture trapdoor structures with horseshoe shaped fractures downsag pits with centroclinal dips locally up to 60 pits with peripheral graben and crevasses piecemeal highly fragmented collapse structures and funnel shaped pits containing disaggregated sediment a sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward dipping ring fracture produces a small diameter pit this is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit and by collapse of overhanging pit walls to produce vertical to inward dipping walls and aprons of collapse debris on the pit floor the various structures have potential for preservation even in regions prone to high rainfall and flooding and they can be used to indicate that former lahars contained abundant blocks of ice

bulldozing and resuspension of shallow shelf sediment by ice keels implications for arctic sediment transport trajectories abstract the orientations and termination directions of newly formed ice gouges identified in a 5 year study of two offshore corridors in eastern harrison bay alasaka indicate a bimodal distribution of sediment transport directions west southwest and southeast due to ice keel bulldozing the westerly sediment transport results from the dominant westward drift of sea ice and ocean currents whereas the southeasterly transport results from episodic fall storms with winds from the northwest transport associated with ice gouging occurs by bulldozing and by resuspension during the bulldozing processes fine grained m sediment transport may also involve transport of resuspended sediment by intensified currents found near the grounded floes leaving behind a lag of coarser sediments in harrison bay about 6000 m 3 of sediment is reworked each year by ice gouging for every square kilometer of the seafloor between water depths of 5 and 18 m over 50 of this sediment is moved onshore to the southeast whereas 35 is moved alongshore to the west the actual distance of sediment transport is dependent upon the grain size of the seafloor sediment coarse grained material 63 m is bulldozed as far as 7 m in the direction of ice movement whereas sediment finer than 63 m may be transported by intensified bottom currents up to 80 times this distance

sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences abstract tills and tillites are defined and subdivided into primary tills comprising lodgement tills melt out tills and sublimation tills and secondary tills comprising flow tills and deformation tills they are defined on the basis of their mode of deposition which endows them with their distinctive properties another category of till that of supra till is defined on the basis of its debris source derived supraglacially from valley sides and nunataks which gives these tills a coarse grained character the processes of till deposition and of outwash sedimentation are associated in several recurrent combinations which allow the definition of three principal glacial sediment associations and land systems which define the character of the sequences within which tills tend to occur the criteria which allow tills of different genesis to be identified and to be distinguished from non till diamictons are reviewed there are several features which are uniquely characteristic of till but unfortunately these are few it has been found generally necessary to employ an array of characteristics which though not individually unique to till when taken together can be strong evidence for particular till types the recognition of several typical and repetitive facies sequences which form in the major glacial sedimentary environments can also be important indicators of till genesis

ice rafting of fine grained sediment a sorting and transport mechanism beaufort sea alaska abstract the presence of turbid sediment rich fast ice in the arctic is a major factor affecting transport of fine grained sediment turbid ice was found to be present in a zone 10 to 20 km wide along the coast of the beaufort sea sediment concentrations observed in cores taken in seasonal fast ice ranged from 3 to more than 1 600 g m3 finely disseminated silt and clay sized particles dominated discoloring the upper segments of the cores in a layer up to 1 m thick in almost all of the cores the upper most 10 cm of ice was relatively less turbid and the relief at the base of the turbid layer was 10 to 20 cm over distances of 1 to 2 m observers have documented the widespread sporadic occurrence of sediment rich fast ice in both the beaufort and bering seas the known sources a d transport relations of suspended sediment did not explain this distribution of turbid ice the occurrence of sediment in only the upper part of the seasonal fast ice indicates that sediment rich ice forms early during ice growth the most likely mechanism for the formation of sediment laden ice and preferential sorting of fine sediments requires resuspension of nearshore bottom sediment during storms accompanied by formation of frazil ice and subsequent lateral advection before the fast ice is stabilized we estimate that the sediment incorporated in the beaufort ice canopy formed a significant proportion of the seasonal influx of terrigenous fine grained sediment the dominance of fine grained sediment suggests that in the arctic and sub arctic these size fractions may be ice rafted in greater volumes than the coarse fraction of traditionally recognized ice rafted sediment the incorporation and transport mechanism may be a significant factor in the transport of fine grained sediments in the arctic basin

the sedimentary record of drifting ice early wisconsin sunnybrook deposit in an ancestral ice dammed lake ontario canada abstract outcrops of pebbly mud diamict at scarborough in southern ontario canada the so called sunnybrook till are associated with the earliest incursion of the laurentide ice sheet lis into mid continent north america some 45 000 years ago the sunnybrook is a blanket like deposit containing deepwater ostracodes and occurs conformably within a thick 100 m succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake contextual evidence associated facies sedimentary structures deposit geometry and landforms indicates a low energy depositional setting in an ice dammed ancestral lake ontario in which scouring by floating ice masses was an important process u shaped iceberg cut scours with lateral berms up to 7 m deep occur on the upper surface of the sunnybrook and are underlain by sub scour structures that extend several meters below the scour base ice rafted concentrations of clasts clast layers grooved surfaces formed by floating ice glissading over a muddy lake floor soft sediment striations and melanges of sand and mud mixed by grounding ice keels ice keel turbates are present and are all well known from modern cold environments the wider significance of this depositional model is that the lis margin lay east of scarborough and did not overrun southern ontario this finding is in agreement with recent data from the erie basin of canada ohio and indiana where deposits formerly correlated with the sunnybrook and thus implying an extensive early wisconsin ice sheet are now regarded as illinoian a speculative hypothesis is proposed that relates deposition of the sunnybrook and two younger deposits of similar sedimentology to surge like instabilities of the southern lis margin

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

preservation of ice formed features in a subarctic sandy beach sequence geologic implications abstract the barrier beach shoreline near michael river labrador is ice bound for more than 6 months each year the contemporary beachface deposits record a complete yearly cycle as follows the lowermost unit d a well laminated fine to medium grained sand and the overlying unit a a graded sequence of well mixed sand and gravel near the bottom and medium grained laminated sand at the top represent foreshore accretion during summer and fall unit a is overlain by unit b a laminated fine to medium grained sand deposit containing contorted and disrupted laminae and intrabedded sand clasts features which characterize middle to upper foreshore deposits that have accreted under freezing conditions the cycle is completed by unit c a mixed gravel and sand deposit that resembles ice rafted and ice push deposits which form on cold climate beaches during spring break up of nearshore ice unit b is considered to be the freeze up deposit formed during early winter and unit c the subsequent break up deposit which accumulated during spring unit c is overlain by unit d a well laminated foreshore sand which marks the beginning of the next cycle the fact that freeze up and break up events are recorded in a yearly cycle of beachface accretion indicates that such deposits could have been preserved in the rock record if the cyclic sequence recorded in the beachface near michael river were encountered in ancient rocks it could be a good indicator of paleo climatic summer winter seasonal conditions

a high resolution record of lateglacial and early holocene marine sediments from southwestern sweden with special emphasis on environmental changes close to the pleistocene holocene transition and the influence of fresh water from the baltic basin a high resolution study of a marine depositional record 43 m long dated by accelerator mass spectrometry from goteborg gothenburg southwestern sweden shows biostratigraphical and sedimentological changes of environmental significance during the lateglacial and early holocene high accumulation rates are recorded from the onset of the deglaciation of the area ca 13 500 yr bp until 10 300 yr bp by which time approximately 100 m of marine sediments were deposited the early holocene is represented by 10 m only of sediment the influence on the skagerrak kattegat coastal area of the dramatic final drainage of the baltic ice lake at 10 300 yr bp is re evaluated its impact on the distal swedish west coast was limited and sediments that were previously related to this drainage are reinterpreted here it is suggested they reflect resuspension and redeposition of sediments from the large inland lake vanern basin between ca 9500 and 9000 yr bp at 10 200 yr bp a general climatic change and a sudden incursion of warm and saline atlantic water into the norwegian sea occurred and the skagerrak altered environmental conditions with more temperate bottom water conditions in the investigation area

development of a new classification system for assessing of rock mass drillability index rdi the drilling process and its results are affected by various parameters of the rock material and rock mass the effects of rock material have been emphasized in various studies however lack of perfect knowledge of rock mass structural parameters may lead to unpredictable results this paper presents a new classification system for specifying the rock mass drillability index rdi for this purpose six parameters of the rock mass including texture and grain size mohs hardness uniaxial compressive strength ucs joint spacing joint filling aperture and joint dipping have been investigated by physical modeling and rated physical modeling in particular has been used for investigating the effects of joint characteristics on drilling rate in the proposed rdi system each rock mass is assigned a rating from 7 to 100 with a higher rating corresponding greater ease of drilling based on the rdi rating the drilling rate may be classified into five modes slow slow medium medium medium fast and fast

stratigraphy and infill history of the glacially eroded matane river valley eastern quebec canada terraces in the lower matane river valley eastern quebec canada were studied to describe the stratigraphic architecture of a glacially eroded valley fill the matane river valley hosted a glacial tongue connected with a regional ice cap during the early opening of a calving bay in the modern st lawrence estuary and was subsequently flooded by the goldthwait sea as the laurentide ice sheet margin retreated stratigraphic sedimentological light detection and ranging lidar and geochemical analyses as well as radiocarbon measurements allowed the identification of four stratigraphic units deposited during and following deglaciation glacial outwash unit i delta bottomsets unit ii delta foresets unit iii and fluvial deposits unit iv stable isotope 13c and c n ratio values reveal the relative influence of the two end members algae and terrestrial plants on organic matter sources between the stratigraphic units climate major relative sea level fluctuations and sediment yield are recogn

quaternary sedimentation of the alaskan beaufort shelf influence of regional tectonics fluctuating sea levels and glacial sediment sources abstract the offshore stratigraphy of the quaternary gubik formation of arctic alaska has been studied on high resolution seismic profiles with a maximum sub seafloor penetration of about 100 m in general marine transgressive subunits of the gubik formation are wedge shaped on the shelf thickening slightly seaward to the shelf break beyond which they are offset by landslides and slumps beneath the eastern third of the alaskan beaufort shelf active folding has created two persistent structural depressions the eastern and western wedge terranes in which the wedge morphology is especially well developed the youngest transgressive marine wedge which was deposited in such a way as to fill these depressions leaving a generally flat present day shelf surface is inferred to be late wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late wisconsin glacial sea level minimum the thickness of this youngest wedge unit a locally exceeds 40 m on the outer shelf yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf lithologies of the gravels are exotic to alaska but similar to suites exposed in the canadian arctic islands these observations suggest a depositional scenario in which the retreating laurentide ice sheet shed sediment laden icebergs from the canadian arctic islands into the arctic ocean following the late wisconsin glacial maximum these bergs were then rafted westward by the beaufort gyre and grounded on the alaskan shelf by northeasterly prevailing winds especially large numbers of bergs accumulated in the wedge terrane embayments created as sea level rose and melted there filling the embayments with their sedimentary cargo as glacial retreat slowed depositional rates on the shelf dwindled this mode of deposition in the alaskan beaufort wedge terranes may be typical of early post glacial transgressive phases throughout quaternary time it has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands and whose seaward termination depths appropriately corrected may yield estimates of lowstand magnitudes knowledge of global sea level fluctuations back through the sangamon interglacial oxygen isotope stage 5e and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the beaufort sea record with major 18 o enrichment maxima in the oxygen isotope curve back through stage 8 in this tentative scheme close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points further testing of the quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the beaufort wedge terranes

micromorphological aspects of glaciolacustrine sediments in northern patagonia argentina in this study the sedimentology micromorphology and structure of four deformation sites in end moraines or near end moraine settings are presented micromorphology has proven to be a powerful tool in the interpretation of the sediments the four sites are related to three of the four major glaciations known from this part of patagonia nahuel huapi anfiteatro and pichileufu all four sites are characterised by glaciolacustrine environments in which sedimentation occurred at least partly on and or against dead ice with the exception of one section in the san martin de los andes area where deformation occured by active ice push all major disturbances faults and folds are the result of dead ice collapse comparison with micromorphological observations on basal tills shows that the sediments all lack a clear subglacial imprint

iceberg deformation and erosion in soft sediments southeast norway abstract trenches in soft glaciomarine sediments have been excavated through two relict iceberg scours one upslope and the other horizontal and through one iceberg gravity crater the scours are 70 and 30 m wide respectively and are 1 m deep the grounding features were formed by current driven icebergs during flooding of previously emergent sea bottom 9200 yrs b p the clay beneath the scours and craters is deformed and small and larger scale folding small faults and thrusts joints fissures and collapsed lamination are found different scouring mechanisms apply for initial phases of upslope scouring and horizontal scouring at the start of upslope scouring the sediment mass is removed by thrusting and the depth of deformation within the subsoil is shallow in horizontal scouring two thirds of the scour depression is due to erosion and one third to deformation of the subsoil the deformation can in this case be detected down to four times the scour depth the current velocities are critical for survival of the plough ridges along the horizontal scour the plough ridges are missing because of current erosion during and after scouring

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

description and numerical model of pleistocene iceberg scours and ice keel turbated facies at toronto canada near toronto in southern ontario canada glaciolacustrine muds and shoreface sands of late pleistocene age early wisconsin glaciation 45 ka were deformed by icebergs ploughing the floor of an ancestral ice dammed lake ontario outcrop mapping and a ground penetrating radar survey identify ice scour structures up to 4 m deep up to 10 m wide and at least several hundred metres long with high standing lateral margins berms ploughing of lake floor sediment is also recorded by ice keel turbated facies in which storm deposited shoreface sands have been mechanically mixed with underlying muds palaeoenvironmental information for one prominent scour such as water depths estimates of the mass and draft of the ice mass and scouring forces can be determined using a simple finite element numerical model a mass of 0 04 million tonnes a keel draft of between 10 and 30 m and a scouring force of 5 103 kn is consistent with scouring by a small iceberg bergy bit or pressure ridged lake ice the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting estimates of ice mass dimensions agree with independent reconstructions of palaeobathymetry no greater than 20 m derived from storm deposited hummocky and swaley cross stratified facies that fill the scour data presented here aid the identification of ice scour structures and turbated sediment in the ancient record despite being a common process on modern high latitude shelves descriptions of ancient structures and facies are few

an objective mapping method for estimating geostrophic velocity from hydrographic sections including the equator objective mapping can remove the equatorial singularity from the problem of estimating geostrophic shear from noisy density measurements the method uses the complete thermal wind relation so it is valid uniformly on and off the equator errors in the thermal wind balance are due to neglected terms in the momentum balance which are treated as noise in the inverse problem the question of whether the geostrophic balance holds near the equator is restated as a need to estimate the size of the ageostrophic noise in the thermal wind equation objective mapping formalizes the assumptions about the magnitudes and scales of the geostrophic currents and about the magnitudes and scales of the ageostrophic terms and measurement errors the uncertainty of the velocity estimates is calculated as part of the mapping and depends on the signal to noise ratio geostrophic density signal to ageostrophic noise in the data as well as the station spacing and the scales assumed for the geostrophic velocities the method is used to map zonal velocity from a mean hawaii tahiti shuttle density section these are compared with previous velocity estimates for the same dataset calculated using other techniques by choosing appropriate scales the objective map can duplicate previous results new temperature data are presented from a repeating high resolution expendable bathythermograph section crossing the equator at about 170 w with four cruises a year between 1987 1991 there appear to be significant differences between this mean temperature and the shuttle mean temperature temperature is converted to density with the aid of a mean t s relation and geostrophic velocity maps are calculated for the 4 year mean the mean geostrophic undercurrent obtained from our sections is weaker than in the shuttle estimate and is centered slightly north of the equator enforcing symmetry about the equator removes the offset of the current giving a stronger but narrow undercurrent the density field apparently includes significant o 0 5 kg m 3 large scale ageostrophic variability which makes velocity estimates from single cruises poorly determined near the equator

ice erosion of a sea floor knickpoint at the inner edge of the stamukhi zone beaufort sea alaska abstract in 1981 and 1982 detailed bathymetric and side scan sonar surveys were made of an area of the sea floor north of prudhoe bay alaska to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone the coast parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic the fathograms and sonographs resolved 10 cm features and electronic navigation gave relocations accurate to about 10 m year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location associated with this ice boundary the bathymetry shows a pronounced break in slope the knickpoint on the shelf profile at about 20 m depth the 2 3 m high knickpoint is cut in a consolidated gravelly mud of pre holocene age a well defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint the sonograph mosaic shows that seaward of the knickpoint ice gouges saturate the sea floor and are well defined inshore the gouges are fewer in number and are poorly defined on the records few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint we believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone intensified currents associated with this boundary winnow away fine sediments ice bulldozing and currents shape the shoals which perch atop the knickpoint the knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone

circular cryogenic structures from the hirnantian deglaciation sequence anti atlas morocco abstract more than a hundred circular structures are observed at the topmost part of the late ordovician glaciogenic record in the central anti atlas southern morocco the structures were formed in the outer glaciated platform and characterize the hirnantian deglaciation sequence they are distributed within a 20 meter thick stratal interval and at present relicts of them still occupy several square kilometers in map view the circular to ovoidal structures which comprise fluvial sandstone beds and are sealed by shallow marine strata occur in closely spaced clusters they are 13 320 m in diameter with half of them in the 40 90 m range stratal wedging and bending as well as extensional and reverse centimeter to meter scale soft sediment fractures demonstrate that formation processes initially involved synsedimentary uplifts subsequent subsidence and collapse resulted in the formation of circular structures which essentially correspond to localized depocenters in the form of small scale sag basins regarding the overall deglaciation context the circular structures are interpreted as periglacial in origin with vertical movements ascribed to cryogenic processes involving the growth and then decay of bodies of segregation ice the size and diameter distributions which are comparable to the recent younger dryas and current lithalsa structures suggest that hirnantian circular features relate to similar genetic processes and can be referred to as lithalsa like structures a conceptual emplacement model is proposed which considers that a long term sedimentary aggradation over the fluvial plain prevented any significant landforms either a bump or a depression from being expressed at the depositional surface at the time of the circular structure formation the hirnantian lithalsa like structures constitute firm evidence for a late ordovician discontinuous permafrost during the deglaciation stage assuming that the late quaternary meridional zonation is valid it suggests the anti atlas was at latitudes in the 55 65 interval if combined with the rare pingo structures described in the literature which attest that coeval continuous permafrost conditions occurred at higher paleo latitudes the moroccan circular structures provide evidence for an alternate south pole position during the hirnantian 444 ma

formes figures et facies sedimentaires glaciels des estrans vaseux des regions froides abstract frost and drift ice are two important processes creating distinctive features in tidal flats of cold regions original sedimentary forms figures and structures and a particular facies characterized by two opposite grain sizes fine and coarse together result from ice action in muddy tidal flats grooves or furrows polished and striated surfaces tracks and trails various drag roll and skip marks circular depressions chaotic microreliefs pushed ridges polygonal nets monroes lenticular bedding and deformations are common to intertidal zones along the st lawrence and the james hudson bay area canada they also occur elsewhere in most tidal flats and on continental shelves dominated by ice a better knowledge of drift ice features in modern tidal flats is needed it is a prerequisite to the discovery of similar features in consolidated rocks the finding of such indicators should improve greatly any interpretation of the paleoenvironmental conditions of deposition

intertidal boulder pavements in the northeastern gulf of alaska and their geological significance abstract striated boulder pavements consisting of planar concentrations of clasts having striated upper surfaces are a common feature of glacigenic deposits but their origin is not well understood laterally extensive pavements are currently forming in the intertidal zone west of icy bay in the gulf of alaska pavements comprise armoured layers of interlocking boulders one clast thick that have been eroded from underlying outcrops of late cenozoic glaciomarine diamictites they originate essentially as lag surfaces along a high energy storm dominated mesotidal shoreline boulder pavements are either flat or show a nucleated plan form where successively smaller boulders have been accreted around a large core boulder nucleation imparts a hummocky surface topography to the pavements and suggests that some form of size sorting of clasts has occurred packing is promoted by repeated tamping of the clast lag by floating masses of glacier ice which become grounded across the intertidal zone at low tide repeated abrasion of the pavement surface by debris contained within ice blocks produces smooth flattened clast upper surfaces and short randomly oriented striations data from icy bay can be used to constrain the origin of laterally extensive boulder pavements exposed in late cenozoic glaciomarine sediments on middleton island the significance of such pavements in the geologic record is that they form along erosional unconformities and may identify sequence boundaries

mega deposits and erosive features related to the glacial lake nedre glomsjo outburst flood southeastern norway abstract in this paper we present a suite of erosional remnants mega deposits and subtle bar morphology that we relate to the outburst flood from the glacial lake nedre glomsjo at the end of the last ice age by using large datasets of airborne lidar data implemented in a geographic information system gis we have mapped flood related features along the glomma and vrangselva rivers in southeastern norway the unprecedented overview of the valley reaches obtained by the vegetation free lidar derived digital elevation models dem has revealed a set of hitherto undocumented landforms persisting erosive lines indicators of the uppermost flooded level are carved into surficial deposits in the hillsides and are found as high as 80 90 m above the modern valley floor by using the indicators as an upper flood boundary we have computed cross sectional profiles showing that the flood in some reaches inundated more than 120 000 m2 of the valley large streamlined bed forms which we interpret as flood bars drape sections of the valley floor some several kilometers long the most morphologically striking pendant bars are developed behind flood flow projections such as bedrock knolls or in lee of a valley bend flood bars occur in the entire study area but are more widespread in the north and generally decrease in size moving in a downstream direction kettle holes and ice block obstacle marks from icebergs arrested during the flood are common these features support the theory of a catastrophic drainage event but also indicate a pattern of differential erosion and deposition that allowed us to interpret palaeoflow on individual bars vast aeolian dune fields in the region are interpreted as a secondary product of the flood as deposits related to the event were mobilised by northerly winds momentarily after the flood waned the dune fields cover an excess of 50 km2 and reveal that the region was a highly active periglacial desert after the flood our mapping highlights the outburst flood s role as a landscape defining event morphological evidence determine the southern fringe of the scandinavian ice sheet to c 15 km north of elverum at the time of the outburst flood from calibrating existing 14c dates we postulate an age of c 10 10 4 cal ka bp for the nedre glomsjo drainage event and the contemporaneous margin of the ice sheet

a distinction between ice pushed and ice lifted landforms on lacustrine and marine coasts study of a small lake second roach pond in maine u s a clarifies the distinction between shoreline features created by ice push which occurs on both lacustrine and marine coasts and those created by ice lift related to tidal action in the marine environment ice lifting occurred as littoral sediments were frozen into the lake ice followed by a rise in water level due to damming of the lake before the nival melt each spring in the period 1905 to 1969 prominent barricades were constructed by this means a classification based on this distinction is proposed ice pushed landforms include ramparts ridges in coarse and fine sediments stone pavements ice keel grooves pushed boulder grooves and tails off promontories ice lift features include boulder barricades perched stones stone garlands and ice keel depressions

dynamic ice wallow relief of northern alaska s nearshore abstract contour maps with 0 5 m depth interval were prepared for a small area seaward of reindeer island a barrier island in the beaufort sea alaska by repeated surveys with very accurate navigation and very close trackline spacing the maps reveal numerous closed depressions and mounds about 50 to 100 m in diameter and 2 to 3 m in relief presumably related to grounded ice floes common in the area year round some of the features were obliterated over the course of three seasons while new ones formed although the depressions resemble kettles they are formed by very different mechanisms we believe that these bedforms represent erosion and deposition caused by a intensified flow around stationary ice floes serving as obstacles and b pulsating currents generated by vertical oscillation or rocking motions of grounded floes in a seaway because sediment transport occurs around the ice not where it directly touches the sea floor the depressions are much larger than the base of the acting floes ice wallow bedforms although not found everywhere are characteristic of arctic nearshore regions with non cohesive sediments and most likely occur in other ice stressed coastal environments in differing degrees the bedforms studied here are highly active and must be considered in planning nearshore construction activities

use of the geostrophic approximation to estimate time varying zonal currents at the equator moored thermistor chains at 2 n and 2 s and current temperature moorings at 0 are used to examine the accuracy of geostrophically estimated zonal velocity on the equator in the eastern 110 w and western 165 e pacific the meridionally differentiated form of the geostrophic balance is used to eliminate large errors due to wind balanced cross equatorial pressure gradients statistical analyses indicate that for time scales longer than 30 50 days the observed and geostrophically estimated zonal velocities are similar correlation coefficients of 0 6 0 9 and comparable amplitudes thus low frequency equatorial current oscillations are reasonably well represented by the geostrophic approximation however the mean currents are poorly resolved with the available array in the eastern pacific the mean zonal speed difference over the 10 month comparison period is 25 cm s 1 at 25 m and increases to 60 cm s 1 at 125 m at 165 e mean differences in the upper 250 m are typically 50 cm s 1 over a 4 month record the principal reason for these large mean differences is that the meridional scale of the mean currents is smaller than the spacing of the moorings comparison of observed and geostrophic velocity profiles obtained from shipboard sampling indicates that meridional spacing of about 1 latitude would be optimum for estimating the zonal velocity

downhole physical property logging for iron oxide exploration rock quality and mining an example from central sweden abstract several physical properties obtained from geophysical logging and laboratory measurements were analyzed in order to characterize iron oxide mineralization and host rocks in the blotberget mining area of central sweden seven boreholes intersecting the mineralization between 300 and 600 m depth in a volcano sedimentary setting were downhole logged for this purpose the downhole logging included full waveform triple sonic natural gamma magnetic susceptibility formation resistivity fluid temperature and conductivity while laboratory measurements consisted of density rock quality designation and magnetite content measurements full waveform sonic data were used for rock quality assessments of the mineralized zones and their host rocks and proved their potential to be used for mine planning purposes the ore bearing rocks are primarily distinguished by increased density and dynamic elastic moduli estimated from the full waveform sonic logging although seismic velocities do not follow a linear increase with the density for the mineralized rocks as expected for igneous rocks it is observed that a strong seismic signal from the mineralization can be expected primarily due to their high density in addition the full waveform sonic data could be used as a proxy for fracture delineations and in situ rock quality assessment for example zones of washed up amplitudes in these data correlate well with zones of poor quality rocks identified by core logging based on the full waveform sonic data seismic attenuation and its reciprocal the seismic quality factor were calculated a decrease in the seismic quality factor was observed at zones with low rock quality designation but also correlated with the mineralized zones suggesting several fracture zones in the mineralization and that the ore bearing rocks might be less competent than the surrounding host rocks eventual rock support and reinforcement might be required for future mining operations full waveform sonic data have the potential to improve rock quality assessments for mine planning and exploration purposes

rock mass characterization for shallow granite by integrating rock core indices and seismic velocity abstract mechanical and geophysical properties obviously vary between rocks and rock masses in general rock mass structures are seldom analyzed quantitatively based on geophysical information in this paper the authors combine data from 278 shallow boreholes and 12 csns engineering geo exploration lines in a granitic area in south china and use the gocad software platform to establish a three dimensional geological geophysical model a quantitative relationship between the rock mass structure and granitic rci rock core index is then established an empirical relationship between the rci and the seismic velocity of the rock mass is also obtained which is helpful for analyzing the features of the rock mass this research improves the quantitative study of rock mass structures using geophysical parameters which is helpful for the prevention of geological disasters along the highway in the granitic area

postglacial palaeoceanography in the skagerrak crucial periods of change in the latest glacial to early holocene palaeogeographic and palaeoceanographic evolution in the skagerrak region are portrayed in four time slice maps on a calibrated age scale at 14 0 kyr 11 2 kyr 10 2 kyr and 8 1 kyr the course of palaeoenvironmental events is set in a high resolution chronological framework using images core md99 2286 and a grid of chirp sonar profiles these maps visualize the complex rapid palaeogeographic and palaeoceanographic changes during the glacialinterglacial transition which is characterized by major changes in circulation sediment sources and depositional processes

integrated geological and geophysical exploration for concealed ores beneath cover in the chaihulanzi goldfield northern china an integrated geological and geophysical investigation was carried out in the near mine areas of the chaihulanzi gold field inner mongolia northern china to determine the south eastern strike extension of the principal mineralized shear system in the search for new resources in this case study surface geophysical surveys played an important role in defining the mineralized structures beneath cover a re investigation of the mine geology by observing the underground exposures of mineralization and its hosting structures coupled with re evaluation and re examination of previous exploration data revealed that the mineralization style at the chaihulanzi gold field is not the skarn type as previously assumed but is structurally controlled by an oblique sinistral shear structure moreover a south eastward shallow plunging mineralized corridor within the principal mineralized shear system was also identified implying that the ore forming fluid flow might move through the mineralizing system from the south east at depth to the north west these new geological findings imply that the mineralized shear system should extend much farther south eastwards along strike beneath cover and thus a conceptual target area was proposed a detailed geophysical survey program involving the application of vlf em stratagem eh4 csamt and gradient ip measurements was carried out to test the validity of the conceptual target orientation surveys on the geologically known line 18 traverse revealed that vlf em and stratagem eh4 were the most effective methods of detecting the unseen mineralized system whereas csamt could only provide low resolution data and ip proved to be unsuitable in this environment due to the ubiquitous presence of graphite bearing schists in and around the mineralized system a follow up systematic vlf em survey highlighted the principal mineralized shear system as a linear conductive belt tracing the principal mineralized system for a further 750 m of strike length beneath cover from the previous exploration limit line 18 stratagem eh4 soundings over six parallel traverses perpendicular to the mineralized trend revealed that the principal mineralized shear structure extends for more than 500 m in the dip direction a strong indication of the presence of potential deep mineralization under the surveyed area detailed modelling of the stratagem eh4 sounding images provided well defined targets for test drilling subsequent test drilling on some of these targets returned encouraging results as several core intercepts of economic gold mineralization were encountered this led to a more extensive drilling and underground prospecting program focusing on deep mineralization south eastwards along the mineralized trend

micromorphology of diamicton affected by iceberg keel scouring scoresby sund east greenland this research was primarily funded by the university of brighton s rising stars initiative and the school of environment and technology research investment fund with supplementary funds awarded by the quaternary research association the funding sources had no involvement in study design in collection analysis and interpretation of data in the writing of the article and in the decision to submit the article for publication

wind driven cross equatorial flow in the pacific ocean abstract a scheme for calculation of cross equatorial flow is presented which permits an estimation of meridional velocity at the equator from hydrographic station data and surface wind stress it is offered to rationalize the observations that surface winds are neither zonal nor spatially uniform at the equator and that large scale patterns exist in the meridional slope of the dynamic height field at the equator using historical data in the equatorial pacific for surface wind stress and dynamic height a large scale estimate of meridional velocity is presented for the upper 2000 m with a zonal resolution of 10 of longitude the flow across much of the central equatorial pacific is northward in the upper 200 m and southward at greater depth southward near surface currents are estimated east of 120 w in agreement with direct current measurements at 110 w the frictional component to the flow although determined only in the vertically integrated sense is included assuming an exponential decay from the

relict ice scour marks and late phases of lake agassiz in northernmost manitoba in northern manitoba intersecting grooves 300 1800 m long are ice scour marks created by the dragging of iceberg keels along rises in the bed of a glacial lake whose water plane was at about 305 m asl the lake was bounded by glacial ice on its northern and eastern margins the occurrence of scours on topographic divides indicates that a single extensive lake thought to be a northern extremity of lake agassiz occupied the area as far north as seal river at the time the ice scours were formed the lake extended as far west as sprott lake and eastwards into the hudson bay lowlands into an area later occupied by tyrrell sea the preservation of the scour marks suggests that the lake drained suddenly ice scour marks are easily recognized on air photographs and provide a means of identifying areas that have been inundated by glacial lakes scours in emerged marine sediment are generally obliterated by littoral processes

bottom currents sedimentation and ice sheet retreat facies successions on the mac robertson shelf east antarctica abstract measurements of water turbidity currents seafloor sediment samples and geophysical data document the sedimentary processes and the late quaternary sedimentary history of a continental shelf valley system on the east antarctic continental margin the valley is up to 1200 m in depth and strikes across the shelf it is interpreted as having formed by glacial erosion processes on the outer shelf sill of the valley northwestward offshore currents with speeds of up to 0 47 m s referenced to 100 cm above the seabed were recorded over a 10 month period such currents are competent to initiate bedload transport of medium sand and formation of small ripple sized bedforms which explains the occurrence of ripple cross bedding observed in some x radiographs of cores a nepheloid layer with concentrations of up to 3 5 mg l was noted at two stations and the available evidence suggests that density flows resulting from the sea ice brine rejection mechanism are competent to entrain shelf bottom sediments episodically sediment cores taken from this environment document the succession of facies resulting from retreat of glacial ice from the shelf during the holocene transgression under low sea level glacial conditions the ice sheet is interpreted to have been grounded on the outer shelf where it deposited a grounding line moraine rising sea level and global warming caused the ice shelf to retreat leaving a sub ice shelf glacial marine mud this is overlain by a laminated to massively bedded ice rafted debris rich facies interpreted as being deposited at the glacial calving front above this is a siliceous mud and ooze facies having a basal age of about 10 000 years bp characterising modern open marine conditions two types of iceberg keel marks on the outer part of the shelf valley are recognised from sidescan sonographs one relict arcuate type formed during the retreat of the ice shelf prior to 10 000 years bp and a second modern elongate type that is presently being formed near the shelf break by iceberg grounding processes this facies succession has been described from other antarctic shelf environments and is probably representative of facies deposited during holocene glacial retreat from the antarctic shelf

late glacial and holocene paleoceanography in the skagerrak from high resolution grain size records abstract high resolution grain size analyses of the ams 14c dated 32 m long core md99 2286 from the northeastern skagerrak were performed in order to study late glacial and holocene paleoceanographic and sedimentary changes all ages in this study are given in calibrated thousand years before present ad 1950 abbreviated kyr unless otherwise noted the distinct ending of ird ice rafted debris in core md99 2286 which was retrieved from a location down current from the final calving ice margin in the region indicates that iceberg calving in the skagerrak ended between 10 6 and 10 2 kyr a clay rich sequence in core md99 2286 deposited between 11 3 and 10 3 kyr is attributed to outflow from the baltic basin across south central sweden the sequence is correlated to similar units from cores along the swedish west coast the onset of this clay rich deposition occurs progressively later in cores further south along the coast supporting a previous hypothesis that differential glacio isostatic uplift caused a southward migration of the baltic outflow from the otteid stenselva to the gota alv outlet a distinct coarsening towards younger sediments in core md99 2286 indicates a hydrographic shift at 8 5 kyr which is correlated to a shift previously reported in the skagerrak kattegat and the norwegian channel this shift reflects the establishment of the modern circulation system in the eastern north sea as a consequence of the opening of the english channel and the danish straits and increased atlantic water inflow and the subsequent development of the south jutland current a general trend of coarsening poorer sorting and increasing variability from 8 5 kyr until the present indicates increasing strength and influence of the variable south jutland current a series of changes from ca 6 3 to ca 3 8 kyr in core md99 2286 reflects strengthening of the jutland current towards the present day sedimentation system in the skagerrak kattegat these changes are correlated to previously reported hydrographic shifts at 5 5 14c years bp in the skagerrak and at 4 0 14c years bp in the kattegat it is suggested that these shifts were separate features of a transitional period related to strengthening of the current system the resulting changes are differently manifested in different parts of the skagerrak kattegat due to the complex circulation system the last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material reflecting a circulation system significantly modified by regional climatic conditions especially the general wind directions and storm frequency over the southern north sea

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

glacial geology of outer bjornoyrenna southwestern barents sea the upper cenozoic glacigenic succession in outer bjornoyrenna bear island trough southwestern barents sea is investigated utilizing data from six shallow boreholes 143 m below sea bed and seismic profiling overdeepened troughs in the lowermost part of a large plio pleistocene wedge at the shelf margin are interpreted as glacial erosion forms this suggests that the overlying succession which basinward attains a thickness of several km was deposited during a period with glaciations large scale possible sand ridges in the stratigraphic lower part of this succession are confined to two north south trending zones parallel to the present shelf break they probably formed in a continental shelf coastal environment with exceptionally high sediment supply and fluctuating relative sea level related to glaciations a core from a channel fill in the lower part of the succession consists of possibly glaciofluvial gravelly sand intercalated with till most of the other cores are dominated by middle and upper pleistocene muddy massive partly fissile diamictons interpreted to be mainly tills undrained shear strength of these cores ranges from about 20 kn m 2 to more than 300 kn m 2 and both underconsolidated intervals compared to the present burial depth are found an underconsolidated interval comprising eemian interglacial biourbated marine sediments overlain by laminated weichselian glaciomarine sediments on the outher shelf is covered by 50 100 m of muddy diamicton this diamicton is suggested to be mainly till deposited by a late weichselian ice sheet which was grounded to more than 500 m below present sea level earlier weichselian ice expansions did not reach the outer shelf based on the stratigraphy in the shallow cores and seismic interpretation we suggest that there have been five major expansions of grounded ice to the shelf break since ca 440 ka the present study suggests that glacial erosion was a major process in the late cenozoic denudation of the barents sea and in large areas perhaps as much as 200 250 m of preexisting strata could have been eroded by glaciers since about 440 ka

wind driven cross equatorial flow in the indian ocean abstractmeridional velocity mass and heat transport in the equatorial oceans are difficult to estimate because of the nonapplicability of the geostrophic balance for this purpose a steady state model is utilized in the equatorial indian ocean using ncep wind stress and temperature and salinity data from the world ocean atlas 2005 woa05 and argo the results show a somali current flowing to the south during the winter monsoon carrying 11 5 1 3 sv 1 sv 106 m3 s 1 and 12 3 0 3 sv from woa05 and argo respectively in the summer monsoon the somali current reverses to the north transporting 16 8 1 2 sv and 19 8 0 6 sv in the woa05 and argo results transitional periods are considered together and in consequence there is not a clear somali current present in this period model results fit with in situ measurements made around the region although argo data results are quite more realistic than woa05 data results

ring structures made by shore ice in a muddy tidal flat st lawrence estuary canada abstract large size ring sedimentary structures occurring in a muddy tidal flat on the south shore of the st lawrence estuary are reported for the first time they range from 15 to 50 m in diameter and occur as isolated features or in groups of 3 to 5 in plan they form well defined circles scattered throughout the higher mud flat some structures are characterized by an inner ring and by a chaotic surface of alternating micro ridges and depressions the outer surrounding mud ridge is a few decimeters high and wide 25 60 cm ring structures occur at the emplacement of icefoot pustules and are related to vertical pressures exerted on the substrate by ice blocks moved up and down by tide motion icefoot pustules form every winter but not necessarily at the same location it is likely that the related ring structures can be fossilized and preserved in the sedimentary sequence consequently they can be of assistance in palaeoenvironmental interpretation

facies and allostratigraphy of high latitude glacially influenced marine strata of the early permian southern sydney basin australia the sydney basin of new south wales australia is a foreland basin containing a thick up to 10 km permo triassic succession the southern margin of the basin exposes strata deposited during late palaeozoic glaciation of south eastern gondwana the early permian wasp head pebbley beach snapper point formations and wandrawandian siltstone were deposited between 277 and 258 ma on a polar glacially influenced continental margin adjacent to ice sheets located over east antarctica and eastern australia sedimentary facies together with related ichnofacies and fauna can be grouped into six facies associations that record marine sub environments ranging from high energy storm dominated inner shelf to turbidite dominated upper slope settings cold marine conditions with near freezing bottom water temperatures are recorded by glendonites ice rafted debris most likely deposited by icebergs occurs in almost all facies associations an allostratigraphic approach emphasizing the recognition of bounding discontinuities i e erosion surfaces and marine flooding surfaces is used to subdivide the early permian stratigraphy into facies successions three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics sediment supply and glacio eustatic sea level variation together sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south western margin of the sydney basin initial marine sedimentation characterized by sediment gravity flows and storm deposited sandstones of the lower wasp head formation occurred adjacent to a faulted basin margin overlying successions within the upper wasp head pebbley beach and snapper point formations record aggradation in inner to outer shelf settings along a storm and glacially influenced continental margin tectonic subsidence and basin flooding is recorded by deeper water turbidites of the wandrawandian siltstone

sea ice scouring on the inner shelf of the southeastern canadian beaufort sea abstract about 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern canadian beaufort sea ice scours were divided into two types based on their morphology multiple scours consisting of a series of parallel scours and ridges and single scours single scours are the dominant type representing more than 85 of the total observations the mean scour depth and width are 0 3 m and 11 m respectively but scour depths of more than 2 m and a scour width up to 345 m were documented the magnitude of ice scouring processes increases with water depth in water depths less than 10 m less than 25 of the seafloor surface is reworked by ice scours this percentage increases significantly seaward of the 10 m isobath being more than 75 in water depths in excess of 12 m a break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring this morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges most of the observed ice scours appear to be reworked especially in water depths of less than 10 m and represent small scale sediment sinks inshore of the 10 m isobath scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near bottom flows during the open water season scour orientations show that the dominant motion of ice during scouring events is east or west which is subparallel to the bathymetric contours and coastline scour terminal push mounds however suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events

sedimentology of an ice contact glaciomarine fan complex nastapoka hills eastern hudson bay northern quebec abstract emerged holocene coalescing glaciomarine fans are exposed along the nastapoka hills eastern hudson bay the fans form part of a regional stratified drift belt associated with terrestrial and submarine frontal moraines and other grounding lines deposits these thick extensive and in many cases coalescent sediment bodies were deposited during a stillstand of the quebec labrador sector qls of the laurentide ice sheet lis that pinned on the hills during eastward retreat from hudson bay the fans are composed of basal interbedded and interlaminated sand silt and silty clay facies association i fa i deposited by suspension settling from overflow plumes sediment gravity flows and ice rafting towards the ice contact zone fa i interfingers with diamict layers fa ii deposited by gravity flows and ice rafting these two sedimentary units are overlain by interbedded sand and gravel fa iii formed by reworking during subsequent emergence parts of fa i and fa ii were remobilized by submarine gravity flows which prevailed long after ice retreat the sedimentology of the nastapoka hills provides information on the processes operating near the grounding line of a temperate ice sheet reaching tidewater

iceberg crater marks on the sea floor labrador shelf abstract sidescan sonograms of the labrador seabed show evidence of numerous subcircular iceberg generated impact craters some of these craters are found in linear associations crater chains having been formed by a single iceberg keel alternately impacting and rotating free of the seabed a three degrees of freedom iceberg model is used to generate crater chain configurations an unstable trapezoid shaped iceberg of 6 million t with a draft of 140 m in a water depth of 160 m is used in the simulations soil pressures acting on the penetrating keel introduce a vertical heave motion which depending on phase relationships with the swinging motions of the iceberg results in a variety of noncoherent crater depths and crater chain morphologies including chains with skips where craters appear to be missing on sidescan sonograms depending on the position of the final static orientation of the iceberg keel it may generate a crater chain if the keel comes to rest above the seabed or a crater chain may lead into a normal scour if the keel remains below the seabed both configurations are observed in nature

monitoring the 1979 1985 equatorial pacific current transports with expendable bathythermograph data geostrophic transports of the major equatorial currents including the equatorial undercurrent and the south equatorial current have been estimated on a bimonthly basis in the central and western pacific over the 1979 1985 period this was made possible by a collection of carefully checked expendable bathythermograph xbt data and a few hydrocast and conductivity temperature depth data this collection considerably improved the number and quality of temperature profiles of the original institut francais de recherche scientifique pour le developpement en cooperation orstom scripps institute of oceanography tropical pacific xbt ship of opportunity program the temperature profiles were first grouped independently of longitude in regions around mean xbt tracks dynamic heights were then calculated relative to 400 db through a t s relationship deduced from the climatological levitus file geostrophic currents were calculated along the roughly south north oriented fiji hawaii and new caledonia japan mean xbt tracks using a specific technique this technique which combines fourier filtering in the meridional direction and in time also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field the filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents using the mean of data collected along 165 e during six tropical ocean and global atmosphere toga orstom cruises finally transports of the main equatorial currents were computed in a subjective way between 20 n and 20 s 0 400 m using monthly charts of geostrophic currents along the two mean xbt tracks the transports in the central pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the hawaii tahiti shuttle experiment in 1979 1980 and during the line island profiling project pacific equatorial ocean dynamics experiment in 1982 1983 reasonable agreement demonstrates that it is possible to use xbt data for transport indexes of the major equatorial currents in the central and western pacific

sedimentary structures made by shore ice in muddy tidal flat deposits st lawrence estuary quebec abstract well preserved sedimentary structures formed by shore ice are exposed in emergent muddy tidal flat deposits along the shoreline of the st lawrence estuary the sedimentary features are exposed in high marsh micro cliffs 1 to 2 m high features from two localities where they are the most abundant sainte anne de beaupre north shore and montmagny south shore are reported here two categories are distinguished first bowl shaped circular and elongated structures 30 to 100 cm across which are former scoured depressions subsequently filled by stratified mud fine sand and organic debris and second deformations folds a few decimeters to a few meters in size produced by ice block pressure pebble to boulder size dropstones are associated with these structures most features were observed in mud flat and low marsh units facies vertically exposed at these localities the age of these tidalite deposits ranges from about 200 to 600 years these ice made structures and deformations well preserved in a sequence of recent emerged tidal sediments suggest that similar features may be preserved in older rock formations consequently they can be considered as a promising tool for interpreting the former climatic conditions in which tidalites and other shallow marine and lacustrine formations may have been deposited

nearshore erosion by combined ice scouring and near bottom currents in eastern hudson bay canada abstract a study of nearshore sedimentary processes was carried out in manitounuk sound a sheltered environment protected by rocky islands along eastern hudson bay high resolution seismic profiles suggest that up to 10 m of holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low energy waves and currents according to our measurements of near bottom currents at 3 7 and 5 6 m water depths the threshold velocity for sediment motion 20 cm s 1 is only seldom exceeded and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone geophysical data seismic and echosounding profiles suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels these data show that the zone of maximum ice scouring between 8 and 12 m water depths corresponds to the zone of maximum erosion of holocene sediments because ice scouring in this area occurs when the sea is largely ice free wind induced near bottom currents probably contribute to the dispersal of the sediments resuspended by ice

observations of sar polarimetric parameters of lake and fast sea ice during the early growth phase abstract this study examines links between two sets of parameters obtained from radarsat 2 quad pol data and geophysical information of lake ice and landfast sea ice in the resolute bay area nunavut canada the first set includes the three orthogonal backscatter coefficients hh0 vv0 vh0 in addition to the total backscatter power span the second set includes polarimetric decomposition parameters obtained using cloude pottier and yamaguchi decomposition methods data were collected during the early freezing period from 20 september until 28 december 2017 meteorological and ice climatological data from the weather station of resolute bay were used to facilitate this task ice thickness and salinity were obtained from established empirical models results show that single bounce and multiple bounce scattering mechanisms are active in lake ice during the entire freezing period while multiple bounce scattering is active in sea ice only during the initial freezing backscatter parameters can be used to determine the thickness of lake ice up to any depth while both backscatter and the tested decomposition parameters are related to the thickness of young sea ice 0 6 is found to be associated with comparable single and multiple bounce scattering mechanisms hence can be used to identify new ice orthogonal backscatter coefficients and polarimetric decomposition parameters provide different information yet their combination offers clues to better identify ice conditions and investigate questions about scattering mechanisms

micromorphology of ice keel scour in pebbly sandy mud and fine grained sands scarborough bluffs ontario canada the keels of icebergs and ice pressure ridges plough through unconsolidated sea lake sediments gouging out long grooves known as ice keel scour marks although the surface and more recently subsurface morphology of scours are well documented little is known of the effect of grain size on the detectability style and intensity of sub scour deformation this investigation macroscopically and microscopically two dimensional thin sections examines suspected ice keel scour in i glaciolacustrine pebbly sandy mud and ii fine grained sands at scarborough bluffs ontario canada in this investigation there is an almost identical suite of deformation structures individual structures and overprinted structural patterns to those identified in icebergscoured clays from former glacial lake agassiz manitoba canada this confirms that deformation in the pebbly sandy mud and fine grained sands at scarborough bluffs is likely to be indicative of ice keel scour discrete differences in the detectability style and intensity of deformation between the scarborough bluffs and glacial lake agassiz sediments are probably a function of grain size in response to ice keel scour this research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes this information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes it also demonstrates the potential value of micromorphology where for example the study of cores is necessary