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

the geomorphology and sedimentology of eskers in north central ireland abstract eskers are common glacial landforms in ireland and form regionally extensive networks that reflect stages of ice retreat of this sector of the late devensian weichselian british irish ice sheet however the sedimentary structures and composition of these eskers are poorly known despite being able to offer valuable insight into subglacial hydrological processes during deglaciation this study presents detailed morphological and sedimentary evidence from six esker systems in north central ireland where adjacent and interacting ice domes were characterized by changes in ice bed thermal and hydrological properties as well as significant ice dome centre migration morphologically esker ridges in this area vary in length size and continuity with some esker systems ascending over hills thus crossing watersheds whereas other systems are confined to basin settings esker systems commonly appear to feed terminal outwash and glaciolacustrine deltas but several systems do not show a clear terminus the internal sediments within eskers vary from concentrically bedded sands and gravels formed within enclosed tunnels to interbedded sands gravels and diamictons occasionally with water induced soft sediment deformations that are likely formed in interlobate settings in contrast with some previous glacier models that assume that esker systems are isochronous and were formed in solely subglacial settings the esker systems described here are interpreted as being of different ages formed in variously subglacial to ice marginal settings and thus cannot be used as a single snapshot of the disposition of ice domes during stages of late devensian ice retreat

the sedimentology of a late pleistocene drumlin near kingscourt ireland abstract an exposure in a late pleistocene drumlin near kingscourt ireland provides a good insight into some of the processes that give rise to such subglacial bedforms the drumlin is located on a ridge cored by red sandstone of carboniferous namurian age which rises to 150 m above m s l the drumlin itself is about 380 m long by 170 m wide and is 20 m in height it is orientated vvnw ese ice flow direction in the area as inferred from general drumlin orientation striae and erratic dispersal was nw se the drumlin is composed of diamicton with four constituent facies containing large scale up to 20 m long and 1 5 m high slabs of the sandstone bedrock which have been displaced tens of metres by ice dragging the thin diamicton matrix is sand rich with few clasts greater than pebble size it contains green sandstone erratics from west and northwest of the study site along with clasts of weathered namurian sandstone which have been sheared from local bedrock the diamicton attains a maximum thickness of 5 4 m the slabs are confined to the basal 2 5 m of the diamicton thus the drumlin is essentially rock cored parts of the matrix are interpreted as injection sediments that have been squeezed into fractures and voids in the bedrock and between rock slabs under high porewater pressures when the ice began to displace fractured substrate deformation structures at a variety of scales are seen in the matrix deformation erosion and deposition were all important in the formation of the drumlin much of the upper part of the diamicton has been sheared subsequent to initial deposition by ice action the sheared units are uppermost in the stratigraphic sequence the shearing is the last glacial process apparent in the drumlin sediment and may have been contemporaneous with drumlinisation both the squeezing process which deposited the injections within the matrix and the deflection in flow of ice were influenced by the obstructing bedrock ridge which in this case is also responsible for the anomalous orientation of the feature

reconstructing the last irish ice sheet 2 a geomorphologically driven model of ice sheet growth retreat and dynamics the ice sheet that once covered ireland has a long history of investigation much prior work focussed on localised evidence based reconstructions and ice marginal dynamics and chronologies with le

response of the irish ice sheet to abrupt climate change during the last deglaciation we summarize 121 14c and in situ cosmogenic 10be and 36cl ages that constrain fluctuations of the irish ice sheet iis since the last glacial maximum lgm that can be linked to abrupt climate changes in the north atlantic region these data provide a robust means to date ice sheet fluctuations because similar age events can be identified from widely spaced sites they are constrained by stratigraphy and they can be related to large changes in the configuration of a dynamic ice sheet the following events are recognized 1 ams 14c ages and 10be and 36cl ages as well as offshore data suggest that the last maximum advance of the iis occurred between 27 and 23 cal ka 2 deglaciation began on the western continental shelf and in the irish sea basin at 23 cal ka dated sites from around ireland constrain subsequent widespread retreat of ice sheet margins from the shelf onto irish coastlines during the cooley point interstadial 20 cal ka ams 14c ages suggest that the cooley point interstadial continued until 18 2 cal ka b p during this interstadial retreat of the ice sheet margin into the northern irish sea basin indicates that the iis may have lost up to two thirds of its mass 3 dated sites from northwestern and eastern ireland indicate that the cooley point interstadial was terminated by ice readvance during the clogher head stadial at 18 2 cal ka 4 the linns interstadial was a brief interval 17 0 16 5 cal ka of ice recession following the clogher head stadial that is identified from raised marine sediments in eastern and northern ireland and cosmogenic ages elsewhere in ireland 5 the iis subsequently readvanced during the killard point stadial reaching its maximum extent 16 5 cal ka indicating that the readvance began sometime earlier 6 widespread retreat of the iis began by 15 5 cal ka during the rough island interstadial 6 readvance of cirque glaciers in western ireland occurred during the younger dryas equivalent nahanagan stadial

sedimentology of a late pleistocene submarine moraine complex county down northern ireland the killard point moraine formed when late pleistocene ice grounded on the isostatically depressed coastal lowlands of county down northern ireland at a time of relatively high sea level the moraine consists of three major lithologic associations which prograded for about 1 km from the ice grounding zone into a glaciomarine environment at the base of the succession a diamicton association is characterized by massive and stratified diamictons that are mainly debris flows it contains a minor ice rafted debris component the overlying sand association was deposited from sediment gravity flows of low to intermediate viscosity the gravel association was deposited by high density sediment gravity flows massive mud beds or drapes occur throughout the sequence and are related to low density turbidity or contour currents sequences of this type are more common in the geological record than the literature suggests and are often explained in terms of terrestrial based deglacial models this calls for a sedimentological reappraisal of many glacigenic deposits which accumulated in areas subject to deep isostatic depression during the late pleistocene

marine debris flows late precambrian tillites of the avalonian cadomian orogenic belt abstract correlative late precambrian strata of the avalonian cadomian orogenic cycle deposited after 670 and before 550 ma are now widely dispersed around the margins of the north atlantic these contain several prominent diamictite horizons long interpreted as tillites within thick turbidite successions associated with volcanic horizons the granville formation of the armorican massif in normandy france contains many pebby mud diamicite beds up to 20 m thick that have been interpreted as glaciogenic regionally the granville formation occurs within the lowest part of the upper brioverian supergroup which consists of several kilometres of turbidites and volcanogenic rocks at granville diamictites can be traced along striked into deformed and intermixed graded conglomerates and mudstones diamictites are identified as debris flows generated on a submarine slope by the emplacement of gravel turbidites on a mud substrate and their mixing during downslope slumping a glacial influence cannot be identified in north america the conception group of the avalon peninsula newfoundland canada contains nearly 4 km of turbidites with a conformable sequence of diamictites the gaskiers formation near its base massive and crudely stratified diamicite beds the diamictite successions of the granville and gaskiers formations provide significant data regarding facies types associations and the geometry of resedimented diamictite sequences in deep marine basins along active plate margins similar deposits at the same tectonic stratigraphic horizon occur in new england and africa this paper emphasizes the difficulty of identifying a direct glacial influence on diamictite sedimentation in such settings and the need for a sedimentological reappraisal of other supposed late precambrian tillites preserved in orogenic belts this is a necessary first step prior to modelling late precambrian paleoclimates

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

streamlined subglacial bedforms on the narke plain south central sweden areal distribution morphometrics internal architecture and formation abstract a flow set of close to 1000 drumlins has been mapped by means of lidar derived digital elevation models and investigated by trenching the area is situated on the sw part of the narke plain and its surrounding uplands in south central sweden which was deglaciated in the early preboreal in a glacioaquatic setting we find that there is considerable morphological difference in drumlin distribution patterns over crystalline basement areas compared to streamlined terrain over palaeozoic sedimentary rock basement the former area is characterized by thin quaternary drift and the drumlins are all of the rock cored type built due to active deposition of sediment around obstacles to glacier flow the latter area is characterized by deep quaternary drift and the drumlins are more elongate and also larger in all dimensions as compared to rock cored drumlins irrespective of these geomorphological differences on local landscape scale we find that drumlin morphometric values remain part of a morphological continuum at the regional scale based on the internal sediment architecture as revealed in two cross drumlin sections we find that the soft cored drumlins were formed by compressional constructive deformation along with excavational deformation along the flanks of the emerging drumlins which shaped the separating troughs intermediate type drumlins are those that demonstrate a coupling between underlying palaeozoic sediment strata in areas of shallow drift sheet these are the result of differing rheological response between incorporated sedimentary rock and a deforming bed below the ice bed interface an overall conclusion is that we find geomorphic and architectural compositional differences between the drumlins and the flowset they form we can closely relate these differences to contextual geological variations with respect to basement type and drift depth we argue that drumlin formation is better explained not by one single unifying process but rather a set of processes erosion deformation deposition by which the subglacial system finds an efficiency equilibrium whereby an obstacle is shaped so that it enhances flow with a minimum of drag i e the typical streamlined form is the result of a positive feedback cycle that tends towards efficiency this approach argues that equifinality is playing a significant role in drumlin formation with a plurality of initial conditions and processes which when combined with a uniformity of specific overriding processes and mechanical properties results in a diversity of morphology and core type at the meso scale and a continuum of landforms at the macro scale

landform modification by palaeo ice streams in east central ireland in eastern ireland subglacial bedforms including drumlins and rogen moraines were modified by headward erosion along two ice streams which had over lapping flow tracks the ice streams which hadtidewater termini are dated by geochrono metric and morphostratigraphic methods to 5 15 0 14 ckyr bp castleblaney ice stream and 13 8 14 ckyr bp armagh ice stream bedforms along ice stream tracks show a morphological continuum which reflects a down ice increase in the degree of modification by ice stream activity i e resulting in unmodified remoulded overprinted cross cut streamlined bedforms the down ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment transport mechanisms bedform and sedi mentary evidence suggest that discrete subglacial meltwater channels which developed up ice changed in a down ice direction to unchannelized flows which deepened towards the ice margin meltwater release from subglacial cavities and produced by strain heating at sheared ice stream margins probably helped support ice stream flow which ended as the volume of subglacial meltwater discharge decreased dated millennial scale cycles of ice activity may be related to instability at tidewater margins followed by complex thermal and hydraulic responses within the ice mass

biofacies and sediments in an emergent late pleistocene glaciomarine sequence skerries east central ireland abstract late devensian sedimentation ca 18 ka b p on the coastal margins of the irish sea basin occurred in shallow water glaciomarine environments around retreating tidewater ice margins high relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last british ice sheet at skerries in east central ireland ice proximal glaciomarine diamict mud sand and gravel facies are selectively preserved in a bedrock depression the coastal exposure about 500 m long can be divided into three lithofacies associations 1 a diamict gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin 2 an overlying mud association was deposited from suspended sediment plumes with minor ice rafting and records ice retreat and increasing distality of the site muds contain a mixed foraminiferal microfaunal assemblage typical of open water shallow marine shelves species can be grouped into reworked temperate cosmopolitan and well preserved boreo arctic elements and indicate mixing of derived and retransported temperate species with an in situ glaciomarine fauna 3 at the top of the section a gravel association derived from a nearshore fan delta rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound this and other sequences elsewhere in the irish sea basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound

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

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

effects of large scale surface topography on ground motions as demonstrated by a study of the san gabriel mountains los angeles california we investigate the effects of large scale surface topography on ground motions generated by nearby faulting we show a specific example studying the effect of the san gabriel mountains which are bounded by the mojave segment of the san andreas fault on the north and by the los angeles basin on the south by si mulating a mw 7 5 earthquake on the mojave segment of the san andreas fault we show that the san gabriel mountains act as a natural seismic insulator for metropo litan los angeles the topography of the mountains scatters the surface waves gen erated by the rupture on the san andreas fault leading to less efficient excitation of basin edge generated waves and natural resonances within the los angeles basin the effect of the mountains reduces the peak amplitude of ground velocity for some regions in the basin by as much as 50 in the frequency band up to 0 5 hz these results suggest that depending on the relative location of faulting and the nearby large scale topography the topography can shield some areas from ground shaking

depositional controls on the magnetic characteristics of lodgement tills and other glacial diamict facies genetic interpretation of massive unstructured diamict and diamictite facies is a commonly encountered problem faced by sedimentologists data are presented concerning the magnetic characteristics namely anisotropy of magnetic susceptibility ams and natural remanent magnetism nrm of facies deposited by 1 lodgement processes at a glacier base lodgement till and 2 subaqueously by pelagic mud deposition and ice rafting rain out diamicts lodgement tills have an nrm that is distorted around the geomagnetic pole position to form a girdle approximately 90 in length either transverse or parallel to ice flow direction this distension appears to be the result of subglacial shear processes because other diamicts deposited passively by melt out below stagnant ice and modelled by a laboratory experiment show a nondeformed nrm clustering around the geomagnetic pole the ams data show that lodgement tills have only a weakly orientated magnetic microfabric glaciolacustrine rain out diamicts show

constraints on the formation and properties of a martian lobate debris apron insights from high resolution topography sharad radar data and a numerical ice flow model

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

sedimentation in a drumlin lee side subglacial wave cavity northwest ireland abstract lee side stratification sequences in a late pleistocene drumlin in northwest ireland are used to assess sedimentation patterns in subglacial wave cavities formed on the lee sides of drumlins three major subglacial cavity sub environments are identified 1 high energy divergent trough like closed conduit characterised by channel fill pebbly sand facies 2 low energy closed conduit characterised by alternating sand silts 3 trough margin dominated by stratified diamicts facies arrangements suggest two major transient states reflecting variations in subglacial meltwater flux the active phase showed meltwater flow directed across the drumlin apex suggesting complete uncoupling from the glacier bed supercavitation as flow velocities waned pebbly sand facies were deposited by in situ freezing of within conduit sediment admixtures the later quiescent phase was characterised by meltwater flow directed transverse to ice flow cavity shrinkage and concomitant deposition of subglacial sheetwash and cohesive sediment flows along cavity margins cavity closure resulted in complete coupling at the ice substrate interface with localised glaciotectonic loading on underlying lee side stratification sequences and concomitant till deposition these late stage sedimentation events at shinnan hill produced a very complex polygene endform which cannot be simply attributed to one formative process more realistically they reflect the influence of a rather complex and very dynamic subglacial system subject to complex spatial and temporal variations in subglacial erosion deposition and meltwater flux at the time of drumlinisation

the interaction between tectonics and mudflow deposits within the main conglomerate formation in the 2 8 2 7 ga witwatersrand basin abstract the black bar is an erosively based unit comprising diamictites overlain by mudstones and interbedded siltstones and sandstones it is situated within the fluvially deposited main conglomerate formation an economically important component of the witwatersrand supergroup the unit is well developed on east rand proprietary mines ltd e r p m situated 25 km east of johannesburg conglomerate reefs angelo leader main reef main reef leader south reef were deposited on erosional surfaces which bound tectono stratigraphic packages the black bar also represents a tectono stratigraphic package in the middle of the main conglomerate formation the main conglomerate formation was deposited during a phase of tectonism which has been associated with nearby marginal faults in previous papers this tectonism manifests itself in the study area as a rising anticline which acted as a syndepositional topographic high over which successive packages were deposited on erosion surfaces regionally the main conglomerate formation forms the base of the central rand group which directly overlies the jeppestown shale subgroup a sequence of fine grained sediments deposited in a large marine or lacustrine water body it therefore marks a rapid transition to subaerial fluvial conditions the black bar extends into the east rand goldfield and is an important stratigraphic marker in the stratigraphy of the main conglomerate formation because of its correlation with the green bar in the carletonville goldfield and the cab in the west rand the black bar facies distribution on e r p m has been used in this paper to explain regional variations between the carletonville and east rand goldfields deposition of the black bar diamictites is attributed to a mudflow mechanism texturally clasts and sand grains are similar to those found in underlying conglomerates and associated sandstones geochemically the black bar has a similar major element composition to the underlying jeppestown shale it is therefore likely that the conglomerates sandstones and shale all acted as source components to the black bar it is thought that tectonic activity and gravitational instability were the important factors in the development of the black bar movements on marginal faults would have increased depositional slopes and triggered slumps and mudflows tectonic uplift on the margin was complemented by basin subsidence this led to a transgression represented by the deposition of turbidites and laminated mudstones and siltstones which form the upper portion of the black bar package this implies that the diamictites like the mudstones were largely deposited subaqueously further uplift reintroduced fluvial conditions with the erosively based main reef leader and south reef packages