development of glacial llyn teifi west wales evidence for lake level fluctuations at the margins of the irish sea ice sheet a thick sequence of quaternary laminated silt and clay sand gravel and diamict has recently been proven at llandudoch st dogmaels west wales most of these deposits accumulated in a tributary valley of afon river teifi that formed prior to the last glaciation the laminated silt and clay occur up to 103 m above present sea level and are considered to have been deposited in llyn lake teifi a large ice dammed lake that developed in the teifi valley as the irish sea ice sheet impinged onto the welsh mainland during the late devensian rhythmic units are interpreted as annual varves whose composition was determined by the distance from the sediment discharge point short term climate fluctuations during the summer months are evident in some of the varve units stratigraphic variations within the laminated deposits are considered to reflect different levels of llyn teifi which varied according to the position of the irish sea ice sheet in the teifi valley and the elevations of three overspill channels the overlying diamict sand and gravel deposits are thought to have accumulated close to the ice front as it encroached into llyn teifi during the final retreat of the irish sea ice sheet a series of kamiform sand and gravel deposits formed along the margins of the glacier

interdune areas of the back island dune field north padre island texas abstract the small young about 100 yrs back island dune field on north padre island south texas consists of fairly persistant oblique dunes up to 6 m high with well developed interdune areas that grade northwestward to small ephemeral transverse and barchan dunes with interconnected interdune areas thence sheet sand areas the subhumid climate is marked by rain associated with frontal systems and tropical storms winds are seasonally bimodal prevailing southeasterly are punctuated by northerly and northwesterly winds with the passage of frontal systems in winter the entire dune field and individual oblique dunes show a net migration of about 15 m yr 1 to the northwest the dunes however are on a seasonally reversing track changing their slipface direction and migration direction with frontal systems one year of monitoring shows sand transport in the dune interdune system to be complex and cyclic during the wind reversals of winter dunes are very ineffecfive sand traps owing to loss of flow separation and much sand is lost to the interdune areas interdune areas store sand during these wet winter months as a result of the wind reversals and higher moisture content during the summer the interdune areas deflate and the dunes build in size the overall dune field deposit appears to consist of three laterally contiguous zones from southeast to northwest 1 continuous climbing oblique dune and interdune deposits 2 discontinuous lenses of dune sand in overall interdune layers and 3 a chaotic mixture of dune and horizontal deposits of the sheet sand areas one year s mapping and trenching documents that interdune sedimentary structures are extremely variable laterally and vertically reflecting specific microenvironments within the interdune flat wet surface features consist of current and wave ripples channel fill miniature deltas wrinkle marks mini ripples rills algae and sand volcanoes abundant adhesion structures rain impacted ripples brecciated surfaces and microtopography reflect damp surface deposits dry surface features are predominately wind ripples others include small isolated barchan and shadow dunes organic debris lag surfaces deflation scours beetle bioturbation plant root structures associated with shadow dunes and grainfall from the adjacent dunes interdune deposits account for about 40 of the total dune field deposits which seems reasonable compared to some ancient examples by virtue of occupying a relative basin interdune deposits are selectively preserved compared to dune deposits in general interdune sedimentation is enhanced by non eolian depositional mechanisms a high water table early evaporatic cements and a variable wind regime the actual thicknesses of individual dune and interdune deposits are less on padre than ancient examples reflecting the relative scale of the bedforms in many respects sequences of sedimentary structure in padre island interdune deposits are typical of ancient coastal interdune strata but some marked departures occur adhesion structures relatively rare in some ancient examples but abundant within padre interdune deposits seem favored by the small size of dune and interdune area the climate and a variable wind regime penecontemporaneous deformation absent in padre interdune deposits but pronounced in some ancient examples probably reflects dune size and the nature of the deposits wavy laminae in ancient interdune deposits probably result from many causes but seem best represented by modern examples of evaporitic algal bacterial formed structures

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 last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

cuspate ore wall rock interfaces piercement structures and the localization of some sulfide ores in deformed sulfide deposits studies on three deformed massive sulfide deposits trojan nickel deposit zimbabwe matchless copper deposit namibia south west africa broken hill silver lead zinc deposit australia show that the interfaces between massive sulfide rock and silicate wall rock are characterized by irregularities and projections of sulfide rock into the wall rock the structures range from simple cusps in which ore layering remains parallel to the ore wall rock interface and to wall rock layering to veins which occupy brittle fractures in the wall rocks in size the features range from minor projections less than 1 m across to major piercement structures which may exceed 50 m in length the structures can usually be related to specific phases of rock deformation in most cases the contained sulfide rock is a tectonic breccia with a foliation parallel to margins of the structure the cusp and related structures reflect competency contrast during rock deformation simple cusps develop in a similar manner to certain types of mullions however where the competent wall rock is relatively brittle ductile sulfides take advantage of brittle fractures and other zones of weakness to penetrate into the wall rock and develop discordant vein structures the mechanism by which the sulfides move is plastic flow although there is some evidence for the activity of a fluid phase the process has economic significance in the generation of locally thickened parts of ore bodies

coarse grained sediment gravity flow facies in a large supraglacial lake near williams lake in the central interior of british columbia the fraser river exposes long sections of late pleistocene glaciolacustrine sediments selectively preserved within a bedrock trough the dominant facies types are thick normally graded gravels and sands that occupy steeply dipping multistorey channels up to 300 m wide and several tens of metres deep channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi continuous surging turbidity flows triggered by catastrophic meltwater discharges into the trough or retrogressive failure of ice cored sediments large scale post depositional deformation structures such as synclinal folds normal faults sedimentary dyke swarms and dewatering structures record gravitational foundering of sediment and pore water expulsion caused by the melt of underlying glacier ice melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub basins within the overlying sediment pile an idealized model of supraglacial lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography

sedimentology of a glaciofluvial deposit at ekeby east central sweden abstract the ekeby site south of stockholm has been chosen to elucidate glaciofluvial sedimentation processes soon after the end of the younger dryas detailed lithofacies and grain size analyses of gravel sand and fine sediment sequences in a gravel pit reflect changes in the depositional environment four main facies assemblages have been distinguished the lowermost part of the sequence was probably deposited in a subglacial conduit environment the middle part of the sequence reflects a transition to a proglacial subaqueous environment the upper part of the latter sequence probably occurred during increased melting of the ice the sequence was then covered by beach gravel formed during the regression after the drainage of the baltic ice lake

the pleistocene succession of the severn estuary a revised model based upon amino acid racemization studies this paper reports the results and stratigraphic implications of amino acid racemization studies of fresh and or inter tidal molluscs from i the important pleistocene sequences of kenn church new blind yeo drain yew tree farm and kenn pier avon county ii the previously undescribed pleistocene beach deposits beneath the llanwern steel mill south wales and iii re prepared and re analysed shells from the th u series dated beach deposits in belle houge cave jersey channel islands these studies indicate the complexity of sea level change in the area in amino acid group ii oxygen isotope stage 5e 120 000 130 000 years bp sea level reached 4 5 m od and possibly 12 m od this episode is correlated with similar group ii beach deposits on the gower coast and freshwater deposits in sw and se britain the data suggest these group ii deposits are different in age from the ipswichian interglacial inter tidal deposits at selsey a group iv age is attributed to freshwater deposits at yew tree farm and kenn pier which collected just above a contemporary sea level or included re worked earlier inter tidal rocky shore faunas these are provisionally correlated with the group iv deposits in the thames estuary at purfleet c 400 000 600 000 years bp since these deposits are thought at post date glacial deposits previously identified at kenn and court hill avon this glacial episode is now regarded as being much older than the wolstonian glacial stage with which it had been correlated previously

an 40ar 39ar thermochronology of the ofoten troms region implications for terrane amalgamation and extensional collapse of the northern scandinavian caledonides fifteen 40ar 39ar cooling ages are reported for metamorphic hornblende and muscovite from far traveled terranes constituting the ofoten nappe stack of northern norway eight cooling ages on hornblende range from 425 to 394 ma and seven muscovite ages from the same or nearby outcrops as the hornblendes range from 400 to 373 ma these data are compared with 40ar 39ar ages from over a large part of the northern caledonides to evaluate regional mineral cooling patterns results indicate that 1 scandian silurian devonian metamorphism was predominant 2 most of the nappes investigated contain some vestige of pre scandian tectonism and or metamorphism 3 hornblende and muscovite cooling ages are progressively younger to the west and south which suggests a hinged to the east mineral cooling pattern and 4 a late out of sequence thrust is the only disruption of this cooling pattern synmetamorphic amalgamation of the nappes resulted from scandian a type subduction the hinged to the east mineral cooling pattern implies isostatic adjustment and exhumation of the footwall of a west dipping crustal scale extensional fault located somewhere west of the present norwegian coast during late synorogenic gravitational collapse the late out of sequence fault formed contemporaneously with uplift in the hinterland implying a kinematic and temporal connection with east directed contractional faulting in the foreland

facies architecture and sequence stratigraphy in glacially influenced basins basic problems and water level glacier input point controls with an example from the quaternary of ontario canada abstract sequence architecture is controlled by two fundamental factors the water level relative to the depositional surface which controls accommodation space and the points or areas of sediment injection which control how this space is filled in relative water level accommodation space and injection points normally vary together and various genetic terms are used to define systems tracts but in glacially influenced basins accommodation space is controlled not only by water level but also by the glacier injection points are similarly dually controlled by water level and by the terminus of the glacier during high lake levels the injection point of the glacier may be underwater at the base of the slope genetic terms like highstand and lowstand therefore are meaningless in successions controlled by sediment input points which are independent of water levels and accommodation space distinct water level and glacier input point systems can occur side by side the water level system controlled by lake level or sea level the glacier input point system controlled by the position of the subaqueous glacier front and both can form juxtaposed systems passing laterally into each other a bewildering and incompatible terminology is needed if the terms of genetic sequence stratigraphy are used for both water level and glacier input point systems because the sedimentary injection points and sequence boundaries of the two systems fluctuate out of phase with one another sequences developed by movement of the glacier are completely independent of those controlled by water levels if genetic sequence stratigraphy is applied to a basin with both lake level and glacier input point systems then each needs separate genetic terminologies to describe them which leads only to confusion however descriptive sequence stratigraphy allostratigraphy can be readily applied to successions like the quaternary of lake ontario we therefore suggest that genetic sequence terms be discarded and simpler allostratigraphic terminology used in glacially influenced basins

some observations on suspended sediment dynamics in storbregrova jotunheimen observations are reported of the dynamics of suspended sediment transport in the meltstream of storbreen in the jotunheimen fine sediment is transferred from the subglacial to the proglacial environment during low flow meltdominated periods and then removed from the catchment during high flow rainfall controlled events both diurnal and storm period sediment load discharge relationships involve clockwise hysteresis but separate multivariate rating curves define variations of load with streamflow according to 1 the relative importance of meltwater and rainfall runoff and 2 changes in the sediment source areas contributing to the stream at different times particle size variations in the suspended sediment also reflect varying source area influences

glacial lake camelsfoot a late wisconsinan advance stage proglacial lake in the fraser river valley gang ranch area british columbia in the gang ranch area british columbia interaction between the regional physiography and ice flow during the late wisconsinan fraser glaciation resulted in the formation of a proglacial lake confined to valleys of the fraser river and its tributaries lithostratigraphic and geomorphic evidence suggests that ponding was initiated in the big bar creek area where the fraser river is confined to a deep canyon in the camelsfoot range during ice advance a proglacial lake system developed that progressively deepened and reached a minimum upper elevation of approximately 710 m asl prior to being overridden by ice we propose that this system be formally named glacial lake camelsfoot a composite stratotype comprising lithostratigraphic units associated with glacial lake camelsfoot is described from eight reference sections along fraser river churn and lone cabin creeks in the gang ranch area additional geomorphic evidence indicates that at the fraser glaciation maximum the cordilleran ice sheet in th

polydisperse suspensions erosion deposition and flow capacity deposition from particle laden flows is often described in terms of the capacity and competence of the flow but robust definitions of these terms have proved elusive in this paper we provide a mathematical modelling framework within which erosion and deposition of polydisperse sediment and thus flow capacity and competence can be rigorously defined this framework explicitly captures the coupling between the suspension and an active layer of sediment at the top of the bed and is capable of describing both depositional and erosional flows over both erodible and non erodible beds crucially the capacity of a flow is shown to depend on the erosional and depositional history because these processes determine the composition of the active layer this dependence is explored within models of bidisperse and polydisperse suspensions it is further demonstrated that monodisperse representations of suspended sediment transport may severely underpredict actual flow capacity the polydisperse model is validated against recent experimental studies of the evolution of suspended material in waning turbulent flows and is used to demonstrate that loss of capacity is the principal driver of sediment deposition

ocean drilling program leg 169s surficial geology stratigraphy and geomorphology of the saanich inlet area southeastern vancouver island british columbia abstract this paper provides i a descriptive overview of the late pleistocene and holocene geology and geomorphology of the region surrounding saanich inlet and ii the palaeogeographic setting for discussion of the oceanographic record at odp leg 169s sites 1033 and 1034 the dominant deposits and landforms in the saanich inlet area are similar to those of late pleistocene marine influenced glacial environments and modern fjord inlets dominated by retreating tide water glaciers patterns of ice retreat meltwater drainage and sea level change are reconstructed for the interval 4000 15 000 calendar years before present yrbp the flux of meltwater and sediment into saanich inlet was greatest between ca 12 000 and 15 000 yrbp at that time sea level was up to 90 m higher relative to land than today during deglaciation tidewater glaciers occupying chemainus cowichan and koksilah valleys entered a marine embayment that formed in the vicinity of cowichan bay satellite channel saanich inlet and saanich peninsula in the early holocene relative sea level fell to a low stand perhaps tens of metres below the present datum and the surface area of saanich inlet and satellite channel was much reduced by the middle holocene sea level had risen to near its present position and modern drainage patterns and oceanographic conditions were established

sedimentation in ice dammed hazard lake yukon hazard lake located in kluane national park the yukon is an ice dammed lake formed in 1966 by the surge of the steele glacier since 1975 it has drained annually by means of a subglacial tunnel during july 1979 observations were made of lake processes before drainage and of sections described in the lake bottom after drainage three facies associations are believed to represent prelake stable lake and annual draining phases gravel commonly found at the base of sections represents deposition in a braided fluvial system prior to 1966 lake sediments deposited between 1966 and 1975 are dominantly graded laminated silt deposited by turbid underflow from the major inflow stream lamination is probably caused by diurnal underflow events or daily variation in strength of underflow no winter clay component of varved sediments is observed during drainage a regressive sequence is deposited as the lake level drops with sand dominated sediments overlapping laminated silt where the main inflow stream en

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

observations on delta forming processes in a fjord head delta british columbia canada abstract the bella coola delta is a laterally confined steep fronted fjord head delta in north bentinck arm in the pacific coast mountains of british columbia the principal controls on sedimentation are 1 the high sediment yield and bedload dominance of the bella coola river which reflect climatic conditions and high drainage basin relief 2 river mouth processes which are controlled by tidal stage and delta morphology and 3 delta front deformational processes which are related primarily to oversteepening in the upper delta front wave processes are of limited significance the large tidal range 3 9 m mean range 5 9 m large range changes the location of distributary outlets at high tide and high discharge frictional forces dominate and the effluent disperses as a plane jet over the delta plain at low tide and high discharge inertial frictional and buoyant forces are important and the effluent disperses over saline basin water subaqueous landslides and debris flows have produced a series of erosional chutes on the delta front

ice action on lakeshores near schefferville central quebec labrador canada ice push action causes considerable shore and vegetation damage on lakes located 10 40 km southeast of schefferville in central quebec labrador the damage occurs mainly on shores of large lakes

sedimentology and depositional model for glaciolacustrine deposits in an ice dammed tributary valley western tasmania australia quaternary sedimentary successions are described from the linda valley a small valley in western tasmania that was dammed by ice during early and middle pleistocene glaciations mapping and logging of exposures suggest that an orderly sequence of deposits formed during ice incursion occupation and withdrawal from tributary valleys four principal sediment assemblages record different stages of ice occupation in the valley as the glacier advanced a proglacial lacustrine sediment assemblage dominated by laminated silts and muds deposited from suspension accumulated in front of the glacier a subglacial sediment assemblage consisting of deformed lacustrine deposits and lodgement till records the overriding of lake bottom sediments as the glacier advanced up the valley into the proglacial lake as the glacier withdrew from the valley a supraglacial sediment assemblage of diamict gravel sand and silt facies formed on melting ice in the upper part of the valley a lacustrine regression in the supraglacial assemblage is inferred on the basis of a change from deposits mainly resulting from suspension in a subaqueous setting to relatively thin and laterally discontinuous laminated sediments occurrence of clastic dykes and increasing complexity of the geometry of deposits that indicate deposition in a subaerial setting a deltaic sediment assemblage deposited during the final stage of ice withdrawal from the valley consists of steeply dipping diamict and normally graded gravel facies formed on delta foresets by subaqueous sediment gravity flows the sediment source for the delta which prograded toward the retreating ice margin was the supraglacial sediment assemblage previously deposited in the upper part of the valley a depositional model developed from the study of the linda valley may be applicable to other alpine glaciated areas where glaciers flowed through or terminated in medium to high relief topography

isostatic adjustments in a full glacial sea during the last glaciation an ice free corridor existed between the northeast ellesmere island and northwest greenland ice sheets this corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea the full glacial sea is characterized by 1 14c dates on in situ marine shells that predate initial emergence unloading followed by 2 synchronous emergence from the marine limit throughout the peripheral depression relative sea level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation these curves also document the history of glacial unloading and the form of the relative sea level curve that one would theoretically expect in the peripheral depression the form of the curves presented here is unlike any other published emergence curves from arctic canada or from fennoscandia the relative sea level curves for northeast ellesmere island show three segme

thermobarometric profile through the caledonian nappe stack of western ofoten north norway p t estimates from pelite thermobarometry along a transect through the caledonian nappe stack in ofoten north norway 68 30 n plot as a trend in p t space ranging from 443 c 6 9 kb to 688 c 10 6 kb the p t range for each nappe overlaps the others except for those from the lowest unit narvik group which has significantly higher values within the p t ranges for each nappe the position on the trend of a given sample is independent of its tectonic position results support our earlier conclusion based on structural and petrographic grounds that the regional metamorphic peak was reached during or after stacking of the nappes in the siluro devonian scandian orogeny

fan deltas and braid deltas conceptual problems the concept of fan deltas has been widely misinterpreted in the geologic literature a true fan delta is defined as an alluvial fan deposited into a standing body of water such sequences are of limited areal extent and are as expected uncommon in the rock record by contrast braid deltas herein defined formed by progradation of a braided fluvial system into a standing body of water are a common geomorphic feature in many modern settings and their deposits are common in the geologic record braid delta sequences are often identified as fan deltas on the false premise that coarse grained deposits in a deltaic setting are always part of an alluvial fan complex the authors find that most published examples of so called fan deltas contain no direct evidence for the presence of an alluvial fan even in examples where an alluvial fan could be documented the authors found that in many cases the alluvial fan complex was far removed from the shoreline separated by an extensive braid plain the authors suggest that such systems are better classified as braid deltas they consider that it is essential to distinguish the environmental setting of true fan deltas from that of braid deltas misclassificationmore will lead to incorrect interpretations of expected facies sandstone geometry reservoir quality and tectonic settings criteria based on geometry vertical and lateral lithofacies associations and paleocurrent patterns should be used to correctly identify and distinguish these depositional systems less

origin of an esker like ridge erosion or channel fill sedimentology of the monington esker in southwest wales abstract a ridge of stratified gravel and sand near cardigan in southwest wales has previously been interpreted as an esker its sedimentology is exposed in sand pits and consists of cross bedded gravel and sand incised into a complex of climbing ripple cross laminated sand interbedded with silt and clay the succession records the progradation of fluvial channels across a former lake floor there is no clear sedimentological evidence that the sediments were deposited in an ice contact setting and therefore the feature should not be called an esker the interpretation favoured here is that the ridge is an erosional remnant either of a formerly more extensive outwash plain or of a kame terrace deposited when the adjacent valley was filled with dead ice recognition of an esker needs to be based on sedimentology and regional setting as well as on geomorphology

metamorphosed carbonate platforms and controls on the genesis of sapphire gem spinel and lapis lazuli insight from the lake harbour group nunavut canada and implications for gem exploration abstract baffin island s lake harbour group lhg a paleoproterozoic granulite facies metasedimentary sequence rich in carbonates contains occurrences of the gemstones sapphire corundum spinel including vivid blue cobalt enriched spinel and lapis lazuli hauyne bearing rock most occurrences of these gem minerals are uniquely metasedimentary carbonates and calc silicate rock while a few spinel occurrences formed from metasomatic reactions between si al rich rock syenogranite or gneiss and marble the metasedimentary corundum spinel and hauyne occurrences have similar protoliths primarily dolomitic marls with a high al si relative abundance interpreted as sandy mud to clay siliciclastic fraction in the protolith kimmirut type sapphire deposits formed via a multi step metamorphic process under three different and specific p t conditions lapis lazuli formation required the presence of evaporites to provide na and possibly s for the blue mineral hauyne in addition to high al si calc silicate rocks spinel also occurs in impure dolomitic marbles with very low k al potential for kimmirut type sapphire deposits is expected to be restricted to metacarbonate sequences proximal to the thrust fault separating the lhg from the narsajuaq arc where retrograde upper amphibolite facies mineralization is most pervasive spinel and kimmirut type sapphire deposits are expected to be found in dolomitic marble sequences rich in calc silicate layers the potential occurrence of lapis lazuli is more difficult to predict but deposits could be identified thanks to large geographical footprints and their color similar gem occurrences or deposits to those in the lhg may be found in other metacarbonate bearing terranes with similar metamorphic conditions and for kimmirut type sapphire a similar metamorphic history aerial hyperspectral and photographic surveys are well suited to gemstone exploration on southern baffin island thanks to excellent rock exposure with minimal sediment or plant lichen cover spectral mapping of dolomite diopside phlogopite and scapolite rich domains in lhg metacarbonate sequences using airborne hyperspectral data is expected to provide exploration targets remote sensing exploration could be used in other metacarbonate bearing upper amphibolite to granulite facies metamorphic terranes found in polar climates arid climates or at high elevation in mountainous regions where such rocks are well exposed with minimal vegetative cover

distribution of bed shear stress in rotating circular flume distributions of bed shear stress across the width of a rotating circular flume with smooth and rough bed surfaces were obtained by measurement and model prediction results with flows over smooth beds showed that the flow in the central part may be considered to be two dimensional and that effects of flow depth over the operating range of the flume are minor for flow depths not exceeding 0 14 m for rough beds the bed shear stress distributions were found to be skewed toward the inner wall this can be corrected if a compensating roughness is added to the bottom of the ring such measures are also effective for flumes with smooth beds measured bed shear stress distributions agreed well with the predicted distributions for smooth beds and reasonably well for rough beds the modified preston tube for measurement of bed shear stress in flows over rough beds was found to give promising results further tests are required to completely define the uncertainty in bed shear stress measurements made with this instrument

review of flanking structures in meso and micro scales a variety of host fabric elements he cut by cross cutting elements ce in rocks defines flanking structures fs on mesoscopic and microscopic scales there has been renewed interest in studying and classifying the fs for their morphologies useful as shear sense indicators and geneses existing non genetic morphologic parameters for the fs are reviewed and two new classification schemes are presented one of these is based on the nature of the ce and whether he penetrates it the other scheme takes account of all the potential combinations of drag no drag and slip no slip of the he deciphering the shear sense of the rock body from fs is complicated because the angular relationship between the ce and the primary shear planes might be opposite to what is found between s and c ductile shear fabrics further single ces can curve and several similar fs occur in reverse forms as with mineral fish the shape asymmetries of microscopic ces indicate the shear sense conjugate fs with non parallel ces with interfering perturbation fields around the ces are more reliable shear sense indicators than fs with single ce during low but increasing bulk strains fs may evolve from one type to another e g from a to s type at high strain fs can resemble intrafolial or sheath fold whether the drag is normal or reverse depends fundamentally on the initial angle between the he and the ce and the relative magnitudes of throw and vertical separation

erosional and mechanical strengths of deposited cohesive sediments erosion tests were run on soft cohesive sediment beds freshly deposited from a concentrated slurry in a large rotating annular flume a total of seven tests were carried out with the bed age varying between 1 8 days and 18 9 days a surface type erosion was observed for the applied shear stress range 0 1 1 pa following the increase in the water flow the erosion rate increases quickly to a peak value and then drops off to approximately zero the eroded depth was less than 8 mm for all beds but the resistance to erosion at a given depth and for a given bed structure increased with increasing bed age this phenomenon was attributed to thixotropy the erosional strength of a given sediment layer is found to be one order of magnitude lower than its undrained and drained mechanical shear strengths measured with innovative testing methods hypotheses are given to explain that difference however at constant density and soil water chemistry the erosional and mechanical strengths seem to be affected by the same factors such as bed age structure and temperature

genesis of an esker like ridge over the southern fraser plateau british columbia implications for paleo ice sheet reconstruction based on geomorphic inversion abstract robust interpretations of meltwater systems operating during ice sheet decay are integral to reconstructing deglacial patterns and style yet over reliance on meltwater landform morphology with limited attention to morpho sedimentary relationships and basin scale geomorphic and stratigraphic context can lead to unreliable geomorphic inversion based paleo ice sheet reconstructions this problem is illustrated by the evolution of young lake esker like ridge yler formed in the young lake basin ylb on bc s southern fraser plateau during decay of the last cordilleran ice sheet cis we integrate data from digital elevation models aerial photographs sedimentary outcrops water wells and shallow geophysics ground penetrating radar electrical resistivity tomography previous interpretations of yler as both an esker and an ice contact poorly sorted stratified deposit emplaced by westerly flowing meltwater imply an eastward retreating ice margin geophysical data from a flat topped component of yler reveal slipface and planar bedded sand and gravel overlying lacustrine sediments characteristic of a hjulstrom delta eastward dipping foresets in a gilbert delta exist at the eastern terminus contextually our observations suggest despite esker like morphology yler was not deposited within a subglacial ice tunnel instead it formed through deposition of subaerial outwash between and or on dead ice in front of a regionally backwasting ice margin the complex deglacial evolution of ylb including a drainage reversal and formation of two glacial lakes supports northwestward backwasting of the cis and dead ice within ylb we conclude that accurate geomorphic inversion of meltwater landforms for deglacial paleo ice sheet reconstruction requires knowledge of landform scale morpho sedimentary relationships and basin scale geomorphic and stratigraphic context

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

new insights on illinoian deglaciation from deposits of glacial lake quincy central indiana abstract the deposits of glacial lake quincy overlie a diamicton associated with the classically defined illinoian limit in central indiana this lake covered at least 180 km 2 with a depth of 20 m and developed when the illinoian ice sheet retreated 15 km from the maximum limit causing lake impoundment against devore ridge overflow from glacial lake quincy eroded across the ridge forming a number of steeped walled outlets a section along mill creek exposes a sedimentologic sequence associated with glacial lake quincy from a subglacial diamicton to ice proximal to ice distal glacial lacustrine sediments we report new optical ages by multiple aliquot regenerative dose procedure for the fine grained rhythmically bedded sediments presumed to represent the lowest energy depositional facies dominated by suspension settling which maximized sunlight exposure in turn optical ages were determined on the fine grained 4 11 m polymineral and quartz fractions under infrared and blue excitation which yielded statistically similar ages optical ages span from ca 170 to 108 ka with the average of 16 optical ages indicating deglaciation at ca 135 ka generally coincident with marine oxygen isotope stage 6 to 5 transition and rise in global sea level

preferred crystallographic orientation development during the plastic and superplastic flow of calcite rocks abstract grain size sensitive flow of fine grained rocks such as are often found in mylonitic shear zones is commonly inferred to be accomplished by grain boundary sliding so that no preferred crystallographic orientation is expected to develop pre existing fabrics are supposed to weaken and grain shapes to remain equant however many fine grained mylonites commonly exhibit marked preferred crystallographic orientation whilst displaying a stable but weak grain shape fabric we have examined preferred crystallographic orientation and shape fabric development during the flow of synthetic ultrafine grained 700 c the strong crystal plastic fabric develops more slowly but is not eliminated through the broad transition into true superplastic flow this is interpreted to reflect an important role of intracrystalline plasticity in the accommodation of grain boundary sliding from experiments designed to investigate the extent of survival or modification of an initial twinning fabric through recrystallization and subsequent hot working it was shown that although the microstructure could be totally annealed the early formed fabric survived even subsequent high temperature crystal plastic or superplastic flow this may explain the frequent occurrence of strong low temperature fabrics in calcite ultramylonites

sakami moraine quebec a 500 km long moraine without climatic control the laurentide ice sheet in eastern canada disintegrated step by step as evidenced by several morainic complexes although commonly interpreted as reflecting climatic events it seems probable that the disintegration simply related to changes in the dynamics of the ice margin without climatic control from the example of the late glacial sakami moraine in quebec formed during the drainage of lake ojibway into the tyrrell sea the concept of a re equilibration moraine already briefly proposed is developed the construction of such a moraine implies a stabilization of the ice front when the glacier margin previously floating or calving in a lacustrine or marine basin is suddenly grounded because of topographic blocking or abrupt drop of water level due to drainage the glacial retreat then pauses until the equilibrium profile of the ice is restored and a morainic accumulation can form during the halt

recent glacial history and rapid ice stream retreat in the amundsen sea microfossil analyses of core top samples from 20 sites in the eastern and southern amundsen sea delimit three biotic provinces which are related in part to the activity of a large ice stream and modern sea ice distribution in recent sediments on the outer shelf planktonic and calcareous benthic foraminifera are abundant but diatoms are rare here low diatom abundances in sediments despite high abundances in the overlying sea ice are attributed to nondeposition caused by ocean currents pine island bay sediments are almost barren of microfossils even though diatoms are abundant in overlying surface waters we attribute this discrepancy to deposition of exclusively non organic sediments beneath a former extension of the floating terminus of pine island glacier which probably retreated from this area during the last century the polynya which occupies this area during present day summers is probably so recent a feature that little or no biogenic sediment has accumulated recent sediments in the eastern margin province between pine island bay and the outer shelf contain abundant diatoms and arenaceous foraminifera high diatom abundances here probably record the presence of the amundsen sea polynya during the last few millennia the presence of a compact diamicton beneath recent sediments on the outer shelf and in the eastern margin province suggests that grounded ice formerly occupied the amundsen sea shelf with ice streams in deep elongated troughs these ice streams may have retreated up to 200 km during the holocene

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

gravity anomaly at a pleistocene lake bed in nw alaska interpreted by analogy with greenland s lake taserssauq and its floating ice tongue a possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial lake aniuk formerly lake noatak in the western brooks range geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30 50 mgal anomaly reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried ice thickness of 700 m or sediment thicknesses greater than 1 km comparable anomalies are not known for other glaciated lacustrine valleys however many fiords do exceed 1 km in depth and crary found one nearly 2 km deep in antarctica in studying this fiord he suggested the probable increased efficiency of excavation directly behind the point where an outlet glacier becomes afloat to form the ross ice shelf and where it thus has a vertical component of motion and a mechanism for debris removal floating glacier ice tongues are now rare in the arctic but they exist in maritime parts of northern ellesmere island and greenland studies of ice movement environment and morphology of another large floating glacier tongue in a perennially frozen lake in the angiussaq mountains of northern greenland suggest that pleistocene lake aniuk could have had a similar environment water temperature and near stable water level and that it could have maintained both a floating polar glacier tongue and a perennial ice cover no direct evidence of efficient excavation was observed in greenland but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the alaskan gravity anomaly

a stratigraphic investigation of the celtic sea megaridges based on seismic and core data from the irish uk sectors the celtic sea contains the world s largest continental shelf sediment ridges these megaridges were initially interpreted as tidal features formed during post glacial marine transgression but glacigenic sediments have been recovered from their flanks we examine the stratigraphy of the megaridges using new decimetric resolution geophysical data correlated to sediment cores to test hypothetical tidal vs glacial modes of formation the megaridges comprise three main units 1 a superficial fining upward drape that extends across the shelf above an unconformity underlying this drape is 2 the melville formation mfm which comprises the upper bulk of the megaridges sometimes displaying dipping internal acoustic reflections and consisting of medium to coarse sand and shell fragments characteristics consistent with either a tidal or glacifluvial origin the mfm unconformably overlies 3 the upper little sole formation ulsfm previously interpreted to be of late pliocene to early pleistocene age but here shown to correlate to late pleistocene glacigenic sediments forming a precursor topography the superficial drape is interpreted as a product of prolonged wave energy as tidal currents diminished during the final stages of post glacial marine transgression we argue that the stratigraphy constrains the age of the mfm to between 24 3 and 14 ka bp based on published dates coeval with deglaciation and a modelled period of megatidal conditions during post glacial marine transgression stratigraphically and sedimentologically the megaridges could represent preserved glacifluvial features but we suggest that they comprise post glacial tidal deposits mfm mantling a partially eroded glacial topography ulsfm the observed stratigraphy suggests that ice extended to the continental shelf edge

marble dykes emanating from marble layers in an amphibolite facies multiply deformed carbonate succession troms northern norway in one of the higher nappes of the caledonides of troms northern norway rare thin dykes of calcite marble lie subparallel to the axial surfaces of folds in multilayered marble beds the dykes emanate from pure calcite marble layers mostly in or close to the hinge zones of these flat lying tight to sub isoclinal f3 folds in many cases they appear to penetrate along the axial surfaces of these same folds and there is an up to 10 angular disparity between dyke orientation and axial surfaces the dykes are considered to have originated and been expelled from parent calcite marble layers either at or shortly after the peak of amphibolite facies metamorphism between the d2 and d3 deformation phases of the scandian orogeny the dykes display a dyke parallel dark grey to white colour banding the origin of which is uncertain at present in thin section an equigranular texture is dominated by 2 3 mm equant unstrained calcite grains with straight boundaries and low t twin lamellae denoting a late stage recrystallization a weak oblique calcite grain shape orientation fabric curves into a dyke parallel alignment along the finer grained margins reflecting the simple shear deformation imposed on the host rock regarding the initiation of these marble dykes it seems likely that a combination of p t conditions and possibly partial melting processes was conducive to generating extreme ductility superplasticity at least locally and that this led to the sudden expulsion of a partially molten carbonate aggregate which had momentarily attained a critical pressure and intruded preferentially along available transient fractures prior to the imposition of the d3 simple shear regime

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

comparison of esker morphology and sedimentology with former ice surface topography burroughs glacier alaska topographic maps ofthe burroughs glacier ice surface and the surrounding land surface from 1948 to 1990 were used to generate subglacial hydraulic head maps and compare esker paths to hydraulic gradients hydraulic gradient at the glacier bed is controlled predominantly by ice surface slope but it is also influenced by the slope of the glacier bed eskers at burroughs glacier have been observed forming in subglacial and englacial tunnels most of the eskers formed in subglacial stream tunnels oriented parallel to the calculated hydraulic gradient where the former ice surface slope and slope of the bed do not coincide the relative influence of these factors on esker paths is analyzed one esker is oriented parallel to the land surface contours and perpendicular to hydraulic head contours implying an esker path controlled by the ice surface slope in another area a set of subglacially engorged eskers trends perpendicular to the land contours directly down the slope of the former glacier bed and parallels the calculated hydraulic head contours these eskers formed beneath thin ice in tunnels that were air filled much of the time and thus the slope of the glacier bed controlled the esker paths in a third area where the hydraulic gradient and glacier bed slope in the same direction a subglacially engorged esker trends down the land slope and the calculated hydraulic gradient most of the eskers at burroughs glacier are

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

esker characteristics in terms of glacier physics katahdin esker system maine the characteristics of large subglacially formed eskers such as the katahdin system are closely related to two special peculiarities of water filled tunnels along the beds of ice sheets 1 the water pressure approximates the weight of the overlying ice and 2 in tunnels that descend and those that ascend less steeply than 1 7 times the ice surface gradient the walls melt producing a sharply arched tunnel cross section whereas in those that ascend more steeply they freeze producing a wide low one the first peculiarity primarily governs the paths of these eskers it causes the tunnels to follow the paths ordinary rivers would follow were the land tipped downglacier 11 times the local ice surface gradient the paths therefore trend in the general direction of the former ice flow but tend to deviate so as to follow valleys and to cross divides at the lowest passes as observed ice surface gradients calculated from path deviations at two localities on the katahdin esker system indicate relatively thin sluggish ice the surface of which lay 200 m below the summit of mount katahdin in agreement with independent geologic evidence the second peculiarity primarily governs the form composition and structure of these eskers strong melting causes a large inflow of basal ice and entrained debris to the tunnel and produces sharp crested eskers of poorly sorted poorly bedded sand gravel and boulders with lithologies like the adjacent till whereas weaker melting produces multiple crested ones of similar composition freezing precludes inflow and produces broad crested eskers of fairly well sorted well bedded more water worn coarse sand with few large clasts ice surface gradients calculated from transitions from the multiple crested type to small areas of broad crested type on the katahdin system agree closely with those computed from the paths at nearby localities an anomalously low gradient calculated from a transition to an area of broad crested type approximately twice as wide and long as the probable ice depth apparently confirms that as expected the basal ice was supported by water pressure over most if not all of the width of the esker

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

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

the late wisconsinan deglacial history of the east central taseko lakes area british columbia late wisconsinan fraser glaciation retreat phase deposits and landforms in the east central taseko lakes area british columbia are used to demonstrate a four phase model of deglaciation during phase i at the onset of ice retreat the cordilleran ice sheet occupied much of the study area blocking southward drainage of fraser river phase ii was marked by the deglaciation of uplands and plateaux meltwater drainage patterns were controlled by stagnating glaciers confined to valleys phase iii commenced as remnant ice in the fraser valley downwasted to between 850 and 760 m elevation at this time interlobate glacial lakes formed in hanging valleys east of fraser river drainage of glacial lakes occurred subglacially and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys these events were followed by decreased sedimentation rates reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase iv postglaciation valley fill was subj

sedimentology and origin of deposits from a small ice dammed lake leirbreen norway this paper describes recent proglacial lacustrine sediments exposed by the drainage of a small probably never more than 0 03 km2 ice dammed lake basin at leirbreen central jotunheimen norway the dominant facies include ripple laminated massive and horizontally stratified sands massive and horizontally laminated silts and irregularly laminated fine sands and silts the major control on lake circulation and the nature and distribution of these facies was an underflow driven by a subglacial meltwater stream which formed the major lake input although much of the sedimentary sequence indicates a pulsatory input the proximal character of this small lake prevented the development of classic varved silts compressional deformation of shoreline sediments was due to winter lake ice push other deformational processes included the grounding of icebergs water escape and syn sedimentary downslope collapse observations from an adjacent small ice marginal lake at leirbreen provide support for several of the inferences drawn from the sediments of the former ice dammed lake

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

transverse supraglacially derived crevasse infillings in a pleistocene ice sheet margin zone eastern poland genesis and sedimentary record abstract the so called crevasse infillings in the marginal zone of the saalian ice sheet in eastern poland are atypical relief forms for lowlands glaciated in the pleistocene they are located on a high of the cretaceous palaeogene substratum and form isolated ridges arranged in trains parallel to the former ice sheet margin i e transverse to the movement of the ice sheet the sedimentary succession of the crevasse infillings consists mainly of undeformed glaciodeltaic deposits we propose a model of the crevasse infilling development in three phases against the background of ice mass dynamics 1 ice sheet advance over a high of the substratum compressive ice flow that bumped against the high s slope and enrichment of the ice with debris 2 an overriding of the substratum high by ice masses a tensional ice flow regime resulted in significant crevassing and 3 ice mass stagnation low energy supraglacial deltaic sedimentation in isolated ponds between disintegrated ice blocks under frozen bed conditions considering this genesis we suggest classifying these forms as kames instead of crevasse infillings

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

a comparison of observed and theoretical postglacial relative sea level in atlantic canada two extreme models of late wisconsinan ice cover in atlantic canada and the northeastern u s a are shown to produce postglacial relative sea level curves that bracket existing field observations at six sites throughout the region this suggests that the true late wisconsinan ice distribution is probably intermediate to the two contrasting reconstructions proposed both ice models predict the existence of four relative sea level zones an innermost zone closest to the centre of glaciation in which relative sea level falls continuously throughout postglacial time an outermost zone in which it rises continuously and two transitional zones in which it first falls and then rises in varying proportions according to the distance from the ice margin the distinctive forms of the relative sea level curves are probably representative of each of the zones and are unlikely to be significantly perturbed even by large local ice readvances they therefore establish patterns with which future field data are expected to conform the form that the geological record of relative sea level change is likely to take within each zone is discussed and promising settings for the collection of new data are proposed the common practice of separating relative sea level into an isostatic and a eustatic component is analysed and shown to be incorrect as usually applied the practice is also shown to be unnecessary because the models discussed in this paper predict changes in relative sea level that can be compared directly with the observations

devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales hambrey michael davies j r glasser n f waters r a 2001 devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales journal of quaternary science 16 5 pp 455 482 rae2008

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

deposition properties of fine sediment this paper describes depositional properties of the fine portion d 0 075mm of the surficial bed sediments taken from the upper st clair river the experiments were conducted using the circular flume facility at the canada center for inland waters in burlington canada tests were conducted under the same initial conditions which involved mechanical mixing following the application of a very high shear stress that resulted in a solids suspension of 200 g l deposition was allowed to occur under five different shear stresses the deposition rate and the floc size were monitored using a laser based malvern particle size analyzer the results were used to estimate the settling velocity as a function of applied shear stress and lapsed time for the selected shear stress

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

re evaluation of the middle pleistocene stratigraphy of herefordshire england lithostratigraphical analysis of remnants of high level poorly sorted gravel remnants in northeast herefordshire has allowed the revision and expansion of the existing regional middle pleistocene stratigraphical sequence to incorporate two new formations the oldest pleistocene sediments in the region the humber formation represents part of a major northerly derived cold stage fluvial system which incorporated the ancestors of the rivers lugg and wye and tributaries of the severn the risbury formation consists of glacigenic sediments which were deposited by a large ice lobe emanating from a welsh ice cap the risbury formation is correlated with glacigenic deposits in the cradley brook valley on the west side of the malvern hills which were formerly ascribed to a pre hoxnian severn valley ice sheet 1998 john wiley sons ltd

the development of flanking folds during simple shear and their use as kinematic indicators abstract we used a numerical finite element simulation to model the formation of flanking folds around rotating planar structures e g veins faults or dykes in a non linear viscous medium during ideal simple shear if the planar structure is much more viscous than its host it does not deform and flanking folds with no displacement along the structure develop their vergence is consistent with the overall sense of shear however if the planar structure is much less viscous than its host strain is concentrated within the structure and a secondary shear zone is developed in which slip is opposite to the overall sense of shear then flanking folds develop that have a vergence which is incompatible with the drag on structure if the deflection of markers is not clearly preserved then such flanking folds can be easily misinterpreted as shear bands indicating a wrong shear sense the deflection of the foliation in flanking folds is very similar to deformed asymmetric pull aparts and can therefore help to interpret these otherwise ambiguous shear sense criteria because our model ideal simple shear boundary conditions fails to describe back rotation of planar structures in rocks we speculate that shear band geometries are indicative for general shear

formation of glaciolacustrine late pleistocene end moraines in the tasman valley new zealand abstract detailed examination of the tekapo formation in the tasman valley new zealand has identified 20 facies and five facies associations these associations are delta foresets and bottomsets sediment density flows ice contact lake sediments with ice rafted debris and resedimentation deposits and outwash gravels interpretation of the sediment landform associations informed by observations at modern glacier termini suggests that the late pleistocene tekapo formation moraines have been formed by downwasting of a more expanded tasman glacier during the early stages of glacier retreat ponds on the glacier surface develop into thermokarst lakes which enlarge and coalesce to form a large supraglacial lake continued downwasting causes the lake outlet river to entrench into the impounding latero frontal ice cored moraine lowering the lake level this exposes lake bottom sediments and forms shorelines on the proximal slopes of the ice cored moraine as the ice cored moraine melts these lake sediments are deformed and deposited against the mt john moraine the observations and interpretations reported here suggest the late pleistocene end moraine is a constructional feature not a structural glaciotectonic feature as suggested by previous studies

monsoon variability and major climatic events between 25 and 0 05 ka bp using sedimentary parameters in the gangotri glacier region garhwal himalaya india abstract gangotri glacier has attracted international attention for its rapid rate of retreat it is one of the best studied himalayan glaciers however there are no unanimous views about the history of climate change for the gangotri glacier we prepared the lithologs textural logs by making two trenches in the kame terraces and analysed it in detail for sediment grain parameters and 14c ams dates to infer the depositional sedimentary environments monsoon variability and major climatic events in the gangotri glacier region the sedimentary parameters and geomorphic analysis revealed that the sediments of the kame terraces are consolidated to semi consolidated stratified very coarse to fine grained layers of sand silt and clay with few gravels and sedimentary structures the sediment size indicating energy of the depositional environment varies from medium to fine sand 1 02 2 26 the standard deviation is poorly sorted 0 89 1 46 which describes that the energy of the depositional environment is continuously fluctuating the positive skewness 0 32 0 98 indicates the excess of finer sediments and dominance of low energy whereas very leptokurtic kurtosis 2 28 4 47 describes the fluctuating energy conditions the present study explains the glacial stages and weak indian summer monsoon ism around 19 5 14 5 13 1 10 1 8 6 7 5 2 2 0 54 0 08 ka bp and warm and intense ism during 23 9 22 7 19 4 1 15 0 05 ka bp the higher percentage of clay in both the trenches around 0 65 0 2 ka bp 1300 1750 ad and higher percentage of silt and low clay content around 1 15 0 55 ka bp 800 1400 ad validates the little ice age lia and medieval warm period mwp respectively

sedimentology of late glacial clays in lacustrine basins central ireland abstract distal bottom sediments of a large ice marginal interdomal lake that covered most of the central part midlands of ireland during the last deglaciation were poorly known recent work centred on two raised bog covered basins confirmed relatively thick distal glaciolacustrine sediments undisturbed samples taken in 100 mm cores enabled thin sectioning and micromorphological analysis to be carried out the upper part of the fine sediment mostly clay which is apparently homogenous at the macroscopic level is shown to have been bedded or laminated and subsequently homogenised by load casting with depth bedding or lamination becomes more common until the whole deposit is very finely and rhythmically laminated turbidites a consequence of density underflows together with coarse sediment rain out and dropstones confirm a likely ice marginal environment the finer sediment towards the top of the sequence reflects increasing distality synsedimentary folding and faulting load casting and water escape structures point to rapidly accumulating sediment in an unstable sedimentary environment the lack of bioturbation is not surprising and apparent minor traces towards the base of the rhythmites seems most likely to relate to synsedimentary faulting

sedimentation in proglacial sunwapta lake alberta the hydrologic and limnologic conditions of sunwapta lake a small proglacial lake in the canadian rocky mountains were investigated with special reference to the sedimentology of this lake discharge and suspended sediment concentrations of the inflowing streams were measured to give estimates of sediment input distribution of large loads of fine glacial sediment is largely by an inflow and wind controlled circulation which commonly fluctuates diurnally the spatial distribution of sedimentation was determined by use of sediment collecting pans placed on the lake bed turbidity currents are rare with only one event monitored in 2 years this event was caused by a burst of highly sediment charged inflow water the rarity of turbidity currents is attributed to the high sediment concentration in the lake water which results from the small size of the lake in relation to the inflow wind generated water movement at the lake floor ranges from 0 0 0 03 m s while the maximum recorded velocity of the turbid

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

sediments of ice dammed self draining ape lake british columbia the glacier damming ape lake has withdrawn from its neoglacial terminal moraines in the lake since early in this century at an average rate of 15 m a as a result the first known drainings of ape lake occurred in october 1984 and august 1986 in each event about 54 of the volume of the lake was lost through a tunnel in the damming glacier most of the remaining water was held in the deep basin of the lake behind partially breached neoglacial terminal moraines as the glaciers have withdrawn the character of the sediments has changed sediments in the deep basin of the lake are varved but the grain size especially of the summer deposits has decreased and rates of sedimentation have decreased from about 4 mm a to less than 2 mm a in shallow water deposition of varved sediments has given way to the deposition of massive sediments at rates of less than 1 mm a ice rafted debris is rare in deep water despite the presence of calving bergs during and following the first draining significant subaerial

sedimentology and clast fabric of subaerial debris flow facies in a glacially influenced alluvial fan abstract a large alluvial fan 2 km2 constructed between 11 000 and 7000 years b p at the mouth of cinquefoil creek in interior british columbia canada is identified as glacially influenced debris flow dominated the fan was rapidly constructed during and immediately after deglaciation when large volumes of glacial debris were resedimented downslope fans of this type are widespread in the glaciated portion of the north american cordillera diamict facies deposited as debris flows account for 48 of the fan volume sheetflodd gravels 37 and other facies 15 diamicts show three facies types crudely bedded facies containing rafts of soft sediment that are attributed to downslope collapse and mixing of heterogeneous glacial deposits these occur within the core of the fan massive and weakly graded inverse to normal diamict facies derived from the downslope flow of weathered volcanic bedrock occur within a well defined bed that can be traced across the entire fan the occurrence of weakly graded facies as lateral equivalents to massive facies within the same bed implies the partial development of turbulent high velocity streams within a viscous debris flow moving over a slope of 6 clast fabrics in these facies show weakly clustered a axes dipping up and downslope comparable to other debris flows and lahars the cinquefoil fan its internal structure and facies provides a good modern analogue for ancient diamictite sequences deposited in areas of active uplift rifting and glaciation

reaction induced fluid flow in synthetic quartz bearing marbles the reaction kinetics and fluid expulsion during the decarbonation reaction of calcite quartz wollastonite co2 in water absent conditions were experimentally investigated using a paterson type gas apparatus starting materials consisted of synthetic calcite quartz rock powders with variable fractions of quartz 10 20 and 30 wt and grain sizes of 10 m calcite and 10 and 30 m quartz prior to reaction samples were hiped at 700 c and 300 mpa confining pressure and varying pore pressures initial porosity was low at 2 7 6 3 depending on pore pressure during hip and the amount and grain size of quartz particles samples were annealed at reaction temperatures of 900 and 950 c at 150 and 300 mpa confining pressures well within the wollastonite stability field run durations were between 10 min and 20 h sem micrographs of quenched samples show growth of wollastonite rims on quartz grains and co2 filled pores between rims and calcite grains and along calcite grain boundaries measured widths of wollastonite rims vs time indicate a parabolic growth law the reaction is diffusion controlled and reaction progress and co2 production are continuous porosity increases rapidly at initial stages of the reaction and attains about 10 12 after a few hours permeability at high reaction temperatures is below the detection limit of 10 21 m2 and not affected by increased porosity this makes persistent pore connectivity improbable in agreement with observed fluid inclusion trails in form of unconnected pores in sem micrographs release of co2 from the sample was measured in a downstream reservoir the most striking observation is that fluid release is not continuous but occurs episodic and in pulses ongoing continuous reaction produces increase in pore pressure which is once having attained a critical value pcrit spontaneously released connectivity of the pore space is short lived and transient the resulting cycle includes pore pressure build up formation of a local crack network pore pressure release and crack closure using existing models for plastic stretching and decrepitation of pores along with critical stress intensity factors for the calcite matrix and measured pore widths it results that pcrit is about 20 mpa patterns of fluid flow based on mineralogical and stable isotope evidence are commonly predicted using the simplifying assumption of a continuous and constant porosity and permeability during decarbonation of the rock however simple flow models which assume constant pore pressure constant fluid filled porosity and constant permeability may not commonly apply properties are often transient and it is most likely that fluid flow in a specific reacting rock volume is a short lived episodic process

the origin and glaciodynamic significance of sandstone ridge networks from the hirnantian glaciation of the djado basin niger the djado basin niger was located beneath the inner part of the late ordovician ice sheet the felar felar formation consists mainly of glaciomarine deposits associated with the major ice sheet recession within the glaciation and is bounded by two glacial unconformities structures corresponding to sandstone ridges are found within the felar felar formation sandstone ridges are several metres high about 10 m wide and hundreds of metres long these structures are organized in extensive anastomosed to subpolygonal networks the association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub glacial conditions for their origin sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the felar felar formation by sub glacial turbulent and pressurized meltwater then subglacial cavities were infilled with sand derived from glacial abrasion sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo ice sheet

rotating circular flume a rotating flume installed at the national water research institute in burlington ontario canada to undertake basic research on cohesive sediment dynamics is described the flume is 5 0 m in mean diameter 0 30 m in width and 0 30 m in depth an annular cover plate ring which can be transversed in the vertical direction fits inside the flume with a radial clearance of 1 5 mm on either side and makes contact with the water surface the flume and the ring can be rotated independently at speeds ranging from 0 to 3 rpm the flume is equipped with a laser doppler anemometer a laser particle size analyzer and a preston tube a set of performance tests carried out in this flume indicate that generation of a nearly two dimensional flow field is possible if both the flume and the ring are rotated simultaneously in opposite directions flows generated by keeping the flume stationary and rotating only the ring were found to contain a strong secondary circulation cell and a large variation of bed shear stress

the pre weichselian glaciations of north west europe abstract in north west europe no evidence has been found for glaciations older than the elsterian the elsterian seems to consist of at least two separate ice advances with a minor interval in between during the elsterian in the area south of the baltic sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity the channels were active until the late elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay during the saalian no comparative channels were being formed three different ice advances can be distinguished within the saalian the stratigraphical correlation of which is to be discussed no convincing evidence was found for any interglacial within the saalian sequence there are good reasons to assume that the ice advances were only separated from each other by minor ice free intervals