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

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

threshold load factor for liquefaction triggering evaluations the vs based chart developed by andrus and stokoe 2000 becomes less conservative when a constant cyclic shear strain c is used for liquefaction triggering dobry et al 2015 where vs shear wave velocity specifically natural silty sands in the imperial valley of california heavily preshaken by earthquakes have a triggering resistance for a given normalized vs significantly higher than uncompacted clean and silty sand fills a higher c is required for triggering in the natural sands than in the fills 0 1 0 2 versus 0 03 dobry et al 2015 reached this conclusion within the usual liquefaction chart format plotting csr 1 4 c 0 v0 1 4 0 65 amax g v0 0 v0 rd versus normalized shear wave velocity vs1 1 4 vs 100 0 v0 0 v0 in kpa the next logical step would be to plot c directly versus vs1 however using c is not practical for several reasons the authors propose instead use of the threshold load factor tlf

the dwyka group in the northern part of kwazulu natal south africa sedimentation during late palaeozoic deglaciation abstract multiple sedimentary sequences up to and over 300 m thick and comprising the late palaeozoic dwyka group in the southeastern part of the african subcontinent were deposited during deglaciation of the gondwana ice sheet attention is focused on the northern part of kwazulu natal in south africa where the dwyka group represented by glaciogenic deposits rests on an uneven surface of archaean basement rocks these deposits occur on the northwestern flank of an elongate pre dwyka crustal downwarp which had a significant influence on the mode of sedimentation as it progressively subsided stratigraphic sections from selected localities in northern kwazulu natal display the thickness variations and marked vertical and lateral lithofacies changes that characterise the dwyka group of this region diamictite consistently occurs at the base of the dwyka sequences but is also interstratified with mainly arenaceous and conglomeratic lithotypes which predominate in the upper 60 160 m these heterolithic sequences reflect sedimentation from a retreating marine ice sheet during a rise in relative sea level which commenced towards the close of the carboniferous period in southwestern gondwana as the margin of the ice sheet receded towards an archaean upland region in the northwest this ice mass was locally grounded and stabilised on bathymetric highs of the irregular basement topography release of glacial debris produced diachronous sedimentary sequences as the ice sheet was temporarily pinned on successive basement highs during its episodic retreat matrix and clast supported conglomerates and associated sandstones testify to a plexus of sediment gravity flow and subaqueous outwash processes that occurred near the grounding line thick homogeneous blanket like diamictite facies in the southeastern and southern part of the region suggest an unimpeded retreat of the sediment laden marine sheet in the deeper parts of the basin rapid dissipation of the ice in the closing stages of deglaciation was followed by accumulation of postglacial muds which mantled the glaciogenic sediments in the northernmost part of the study area proximal products of deglaciation represented by conglomeratic deposits and associated sandstones are preserved in deep partly exhumed glaciated valleys and depressions along the southern periphery of the archaean upland the distinctive character of the dwyka group in northern kwazulu natal is partly attributable to the complex tectonic setting in which it occurs and reflects an interplay of various factors that controlled the styles of sedimentation during deglaciation

late pleistocene glacimarine record in saanich inlet british columbia canada abstract late pleistocene deposits were cored at two sites in saanich inlet and provide a record of the sedimentary environment during deglaciation of this fjord at site 1033 at the southern end of the fjord 59 3 m of late pleistocene sediment was obtained in a hole drilled to 105 1 mbsf at site 1034 4 8 km to the north a hole was drilled to 118 2 mbsf recovering 49 8 m of late pleistocene sediment sediments were deposited in this deep 200 m fjord basin as a lobe of the cordilleran ice sheet retreated at the end of fraser glaciation this is the first recovery of basin fill sediments from the pleistocene retreat of the cordilleran ice sheet lithofacies analysis particle size measurements and 17 ams 14 c dates on marine shells or wood fragments are used to reconstruct the glacimarine sedimentary environment sediments are dense gray to olive gray terrigenous silty clay with thick graded sand beds and interlaminated fine sand and silt with mud scattered dropstones clusters of pebbles and pods of sand and granules are common bioturbation indicated by disruption of laminae and horizontal burrows or black mottles is minimal to moderate and decreases downcore a calving tidewater glacier retreated northward through saanich inlet however the ice contact sediments are beneath the depth cored at both sites the glacier retreated rapidly and the basin was open to marine exchange through satellite channel prior to 13 270 60 14 c yr bp the oldest date from the cores deposition of lithofacies association i occurred in an iceberg zone depositional environment dominated by turbid meltwater plumes and intense iceberg rafting within approximately 10 km of the glacier terminus after the glacier grounded at the head of cowichan bay lithofacies association ii was deposited in the ice distal depositional environment by turbidity currents that by passed the sill and turbid meltwater plumes lithofacies association iii was deposited under post glacial conditions at the end of the pleistocene

late wisconsinan glaciomarine deposition and isostatic rebound northern puget lowland washington the distribution and age of glaciomarine and marine sediment in the northern puget lowland washington demonstrate that rapidretreatofcontinentalice theeverson marineincursion andhighratesofisostatic reboundoccurredbetweenabout13 600and 11 300 14 c yr b p 11 3 ka glaciomarine and marine deposits are thickest in zones where retreating ice lobes grounded in the northeast puget lowland and near large drainages glaciomarine sediment was depositedmainlyfrom 1 submarineoutwash in ice proximal zones 2 turbid underflows dispersed melt water icebergs and resedimentation in transitional zones and 3 dispersedmeltwaterandcurrentsinicedistal zones marine estuarine and emergence intertidalandbeach faciesaccumulated in areas more than 10 km from ice margins particularly near major rivers molluscan and foraminiferal assemblages intheglaciomarineandmarinedepositsindicate that turbid cool brackish water covered much of the puget lowland during the everson interval water was generally shallower 30 m in the southern part of the area and deeper 15 60 m to the north mineralogy and geochemical properties such as boron or sodium content of the gravel free fraction do not clearly distinguish glaciomarine and marine deposits from terrestrial deposits isostatic rebound rapidly lifted the glaciomarine and marine deposits through sea level between about 13 5 and 11 3 ka the presentaltitudesofradiocarbon datedshell and the marine limit show that initial rates of isostatic rebound exceeded 10 cm yr 21 in thenorthernpugetlowland butdroppedto 2cmyr 21 before 11 ka the uplift gradient is about 0 6 m km 21 to the north and steepens locally to at least 1 3 m km 21 the pattern of emergence in the northern puget lowland is anomalous locally perhaps as a result of complex isostatic effects near the glacier margin rapid rise of sea level or tectonic deformation

volcanosedimentary paleoenvironments of ediacaran fossils in newfoundland a new perspective on paleoenvironments of ediacaran fossils of the upper conception group newfoundland comes from geochemical and sedimentological study of volcanic tuffs and sedimentary rocks tuffs in the conception group have major and trace element compositions and u pb ages comparable with those of source volcanics on the nearby burin and bonavista peninsulas and the islands of st pierre and miquelon loss of silica and alkalies in some ashes indicates weathering on land not marine diagenesis volcanic crystal and lapilli tuffs fail to show grading and have lapilli and highly vesicular scoria scattered in a fine grained matrix and so they were deposited on land not in water these as well as block and ash flows volcanic spindle bombs and degassing features are evidence of eruptions from nearby subaerial volcanic edifices the fossiliferous conception group accumulated within a forearc basin formed on continental crust inboard of the holyrood horst and uplifted as part of an ancient subduction complex or accreted terrane like analogous forearc basins in oregon washington southern chile and japan the conception group includes not only marine bay turbidites but also a variety of intertidal and terrestrial tsunamites seismites tempestites and paleosols traditional marine turbidite models explain deposition of the mall bay lower drook and lower briscal formations of the conception group but the gaskiers upper drook upper briscal and mistaken point formations were deposited in coastal plains and intertidal zones paleoenvironments of vendobiont fossils preserved in life position in newfoundland were terrestrial to marginal marine not deep sea

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

timing and depositional environments of a middle pleistocene glaciation of northeast england new evidence from warren house gill county durham at various times during the quaternary north eastern england was a zone of confluence between dynamic ice lobes sourced from the pennines northern scotland the cheviots and scandinavia the region thus has some of the most complex exposures of middle to late pleistocene sediments in britain with both interglacial and glacial sediments deposited in terrestrial and marine settings we investigated sedimentary sequences exposed on the coastline of county durham at warren house gill and present a new model of british and fennoscandian ice sheet interaction in the north sea basin during the middle pleistocene the stratigraphy at warren house gill consists of a lower diamicton and upper estuarine sediments both part of the warren house formation they are separated from the overlying weichselian blackhall and horden tills by a substantial unconformity the lower diamicton of the warren house formation is re interpreted here as an mis 8 to 12 glaciomarine deposit containing ice rafted lithics from north eastern scotland and the northeast north sea and is renamed the ash gill member it is dated by lithological comparison to the easington raised beach middle pleistocene amino acid racemisation values and indirectly by optically stimulated luminescence the overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity they are named the whitesides member and form the uppermost member of the warren house formation during glaciation ice rafted material was deposited in a marine embayment there is no evidence of a grounded onshore scandinavian ice sheet in county durham during mis 6 which has long been held as the accepted stratigraphy this has major implications for the currently accepted british quaternary stratigraphy combined with recent work on the middle pleistocene north sea drift from norfolk which is now suggested to have been deposited by a scottish ice sheet the presence of a scandinavian ice sheet in eastern england at any time during the quaternary is becoming increasingly doubtful

palaeoproterozoic glaciomarine sedimentation in an extensional tectonic setting the honkala formation finland abstract the honkala formation of the honkajarvi group in the kainuu schist belt of northern finland central fennoscandian shield provides evidence of palaeoproterozoic glaciation on the fractured surface of the craton the diamictites and associated rocks of the honkala formation are some 190 m thick in the studied area they consist of a remnant of the glacigenic sequence deposited during an incipient stage of crustal extension the rocks rest unconformably on the late archaean basement and conformably on rift related volcanics the volcanics were erupted during a period of general fragmentation and rifting of the late archaean basement 2 4 2 3 ga ago at this time shallow intracratonic basins and depressions started to form on a continental scale subsequently many of these basins subsided below sea level the lower part of the honkala formation consists of turbiditic non glacial mudstones and sandstones up to 70 m thick glacial advance is indicated by ice rafted deposits forming a succession of some 10 to 50 m deposition took place in a glaciomarine rift basin extending towards the interior of the archaean craton waning glacial influence is indicated by some 70 m of sandstones the uppermost sandstones were influenced by intermittent chemical weathering indicating that these deposits were subjected to subaerial conditions and warmer climate correlation on a global scale is possible during the early palaeoproterozoic the fennoscandian and north american cratons were probably situated close together at a high latitude and both were affected by a major continental glaciation the fennoscandian craton then shifted to lower latitudes whereas the north american cratonic margin recorded further glaciations at high latitudes

preparation and analysis techniques for studies of laminated sediments laminated sediments commonly represent the highest resolution continuous records available of marine and lacustrine variability to exploit this information effectively careful sampling and preparation procedures must be followed thus the method of analysis chosen must have sufficient resolution to recover the data the scanning electron microscope because of its good spatial resolution is an ideal tool for analyzing laminated sediment fabric backscattered electron imagery produces preserved flux data on intra annual time scales which enables high resolution fabric studies palaeoenvironmental reconstructions and compilation of data for time series analysis this contribution summarizes the techniques used for laminated sediment fabric investigation and discusses the use of the scanning electron microscope including the best preparation method for thin sections and the procedure for backscattered electron imagery analysis

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

coeval brittle and ductile deformation beneath the late wisconsinan puget lobe washington state usa late wisconsinan glacial sediments exposed on whidbey island and camano island puget sound washington state usa were deposited in a proglacial shallow marine outwash environment during northward retreat of the puget lobe of the cordilleran ice sheet sediments mainly comprise massive and cross bedded sand and gravels and rhythmically bedded clay and silt fine sand couplets interbedded with diamictons that were deposited by a range of mass flows of different viscosities although sediment stratigraphy and ice advance retreat patterns are well established for the puget lobe brittle and ductile deformation structures within and separating these sediment units are less well understood these structures record the nature of ice bed interactions taking place in subglacial and proglacial environments this study examines evidence for these processes and environments key deformation structures identified include open to overturned folds normal and reverse faults clastic dikes and hydrofractures and passive loading structures evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes sediment rheology and sediment system responses to changes in strain caused by ice bed interactions

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

ostracod faunas in a large late pleistocene ice dammed lake southern ontario canada abstract in the lake ontario basin of mid continent north america near toronto canada a low diversity micro crustacean ostracod community dominated by candona caudata and candona subtriangulata occurs in several poorly sorted pebbly mud diamicts units sunnybrook seminary and meadowcliffe tills the diamicts were deposited in an ancestral ice dammed lake ontario with a level at least 90 m above the modern lake during the early and middle phases of the wisconsin glaciation 25 000 75 000 yr b p poorly sorted sediments accumulated by ice rafting and mud deposition from meltwater plumes and are separated by shallower water deltaic facies comparison of the modern habitat ranges of ostracods specifically their water depth temperature and dissolved oxygen preferences provides important palaeolimnological data regarding late pleistocene ice dammed lakes

glaciomarine facies from the western sector of the last british ice sheet malin beg county donegal ireland the coastal margins and mountainous core of county donegal republic of ireland have been areally scoured and deeply eroded along structural lineaments by major late devensian ice streams which moved generally westwards onto the continental shelf a raised glaciomarine sequence is selectively preserved along a gully at malin beg and comprises mud muddy diamict sand and diamict 1 the mud which was deposited from suspended sediment plumes passes upwards into muddy diamict which reflects an increase in ice rafting the muds contain a redeposited foraminiferal assemblage of ice proximal origin pumped into the water column by jets reworking previously deposited outwash the presence of middle devensian shells have been identified from the mud by amino acid analysis this suggests a late devensian age for the succession 2 the overlying sand indicates an increase in traction current activity at the site 3 there is a sharp planar contact between the sands and the overlying tabular diamict unit 4 a surficial sheet of coarse grained breccia is attributed to intense periglacial weathering along the slopes of leahan mountain this sequence and those at other sites in western ireland e g belderg co mayo provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north western margin of the last british ice sheet directional indicators including drumlin fields and major troughs indicate that the north western sector of the ice sheet was drained by major ice streams these ended in calving bays ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines ultimately calving led to accelerated ice flow and areal down draw and collapse of the north western sector of the ice sheet

rhythmically bedded glaciomarine sediments on whidbey island washington abstract several facies of late pleistocene glaciomarine sediments on whidbey island washington are rhythmically bedded the first consists of stratified silty sand which fines upward transitionally into pebbly mud several successions each approximately 0 6 m thick comprise a proximal meltwater facies thought to have been deposited in a shallow 10 m submarine fan environment both the positive lobe shape morphology of the exposure and the inferred depositional processes support this view underflow currents either high concentration turbidity currents or grain flows are thought to have deposited the silty sand while flocculation settling from turbid overflow and or interflow plumes and ice rafting were responsible for pebbly mud deposition such inferences are based on text ral analysis and observations of sedimentary structures the rhythmic interbedding is explained by invoking seasonal fluctuations of meltwater discharge this caused a variation of depositional process in areas proximal to meltwater input into the basin rhythmic interbedding is also observed within a channelized sequence of gravel sand and mud which comprise a fining upwards succession that includes turbidites laminations of sand and silt found in the upper portion of this section closely resemble the type of varved bedding commonly reported from glaciolacustrine sequences

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

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

delta slope processes and turbidity currents in prodeltaic submarine channels queen inlet glacier bay alaska large submarine channels lead away from the coarse grained fjord head delta in queen inlet glacier bay alaska coarse sediment loads from carroll glacier are transported down the delta foreslope and through the submarine channels and finer material is dispersed throughout the fjord from overflow plumes slides and slumps occur intermittently on the delta foreslope a recording current meter positioned in a submarine channel 1 m above the bottom and 2 7 km seaward from the delta brink indicated during july 1989 predominantly quasi continuous downfjord currents although several small surges were also observed flows occurred throughout the daily tidal cycle in both neap and spring periods for intervals of up to several hours often beginning and ending rapidly current velocities ranged from 0 to 120 cm s 1 averaging 12 cm s 1 over one 56 h period and 16 cm s 1 over a 13 h period suspended sediment concentrations 1 m above bottom commonly exceeded 2 g l 1 and attained 8 2 g l 1 the density added to

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

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

criteria to distinguish between subglacial glaciotectonic and glaciomarine sedimentation i deformation styles and sedimentology abstract this paper compares and contrasts the sedimentology and structural geology of a quaternary glaciomarine site melabakkar asbakkar iceland and a quaternary subglacial glaciotectonic site west runton uk research suggests that the glaciomarine environment is dominated by sedimentary processes related to sediment supply water content and distance from the glacier margin glaciotectonic deformation however is dominated by deformational processes related to effective pressure shear strain nature of the subglacial material and distance from the glacier margin from this study a series of criteria are suggested to distinguish both quaternary and contemporary glaciotectonic and glaciomarine environments in addition the paper also discusses the subsequent effects of glaciotectonic deformation on a primary glaciomarine site due to a glacial readvance

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime