the origins of s forms form similarity process analogy and links to high energy subglacial meltwater flows abstract this paper first presents the history of ideas on s form formation with an emphasis on meltwater models the main approach is based on form similarity between modern erosional marks and subglacial s forms form similarity is then extended to process similarity which promotes understanding of s forms three classes of erosional marks are identified obstacle scours basin shaped erosional marks and landforms related to escarpment flow identification is based on form with recognition of elements though it mainly depends on recognition of the whole form in much the same way as we recognize family members or familiar flowers flow conditions related to the various flow features are determined by flow visualization and computational fluid dynamics some s forms are produced in flume models though most are natural features observed in the field examples from beneath past ice sheets are seen in the field and illustrated by air and ground photographs satellite images and dem digital elevation model the results of this work show remarkable similarity between modern erosional marks and ancient subglacial s forms consequently established processes are attributed to ancient forms in turn s forms may be used abductively to interpret subglacial hydrological conditions the lack of waning stage bedforms scoured into primary forms suggests that erosional marks form under abruptly terminating catastrophic flow

geochemical compositions and depositional conditions of upper jurassic and lower cretaceous yorkshire clays england fifty three samples from the oxford kimmeridge and speeton clays of the yorkshire area have been analysed petrographically and geochemically by x ray diffraction x ray fluorescence atomic absorption and combustion toc major elements and the following trace elements have been determined rb sr ba cr v co ni cu zn and mo p 2 o 5 rb ba cr and v show positive correlation to the clastic fraction quartz feldspar and clay minerals cao mno and sr and to a lesser extent ni cu and zn seem to be positively correlated to calcite while fe 2 o 5 mno mgo and co are linked to siderite stratigraphical variations of element element ratios have been used to obtain sedimentological information from the petrographical and geochemical data the oxford clay with its coarse and immature clays was deposited in a regressive development an upwards shallowing with ventilated deposition of more mature and altered clastic material took place throughout the unit during deposition of the kimmeridge clay more reducing conditions existed and finer grained smectite rich sediments were formed the fine grained speeton clay was deposited during changing depositional conditions varying ventilation in a generally regressive development several sedimentological breaks characterize the unit

striated clast pavements products of deforming subglacial sediment studies of modern glaciers have recently drawn attention to the importance of subglacial sediment deformation to glacier dynamics and processes inferences regarding the probable shear strength of this sediment imply that large clasts may in some cases sink to underlying rigid sediment where abrasion by overlying deforming sediment could occur this scenario provides a formative mechanism for striated clast pavements commonly described from the base of fine grained massive diamictons associated with the late pleistocene laurentide ice sheet such a mechanism indicates that at the time of formation of clast pavements overlying diamictons associated with pavements had a low yield strength 0 5 kpa and were deforming mechanically like a debris flow clast pavements may therefore be an important criterion for recognition of sediments deposited by subglacial deformation transport

history of late glacial runoff along the southwestern margin of the laurentide ice sheet abstract the routing of runoff from the retreating laurentide ice sheet was controlled by a combination of ice marginal position and topography isostatic depression also played an important role in the evolution of the ice marginal landscape a major redirection of drainage occurred after ice retreated north of the missouri escarpment about 12 ka bp runoff that had previously flowed south to the missouri river could then be routed eastward to lake agassiz which in turn drained to the upper mississippi river valley changes in drainage routing in the region west of glacial lake agassiz typically were abrupt as new and lower paths along the retreating ice margin became available each new basin was larger than its predecessor and its headwaters extended farther west four distinct sequential phases of ice marginal drainage occurred between 12 and 10 7 ka bp the james sheyenne souris pembina and qu appelle assiniboine starting with the qu appelle assiniboine phase about 11 2 ka bp lake agassiz collected runoff from as far west as the rocky mountains by about 10 7 ka bp ice had retreated north of the lower reaches of the saskatchewan river allowing meltwater to by pass the qu appelle assiniboine basin at about the same time the eastern outlets of lake agassiz opened initiating drainage to the north atlantic ocean from this vast region drainage routes evolved by a common sequence of events beginning with the impoundment of proglacial lakes along the ice margin most of these lakes drained catastrophically resulting in the formation of spillways with distincitve geomorphic features that include broad scoured and streamlined subupland channels along with subsequently incised narrow deep inner channels characteristic deposits of these outbursts include boulder mantles on subupland channel floors boulder gravel bars within the inner channels and large primarily subaqueous fans in lake basins that received the flood bursts these outbursts progressed from basin to basin causing the drainage of other proglacial lakes until they reached lake agassiz spillways associated with the next younger drainage phase were commonly incised across the abandoned lake floors

rift basins in western margin of india and their hydrocarbon prospects with special reference to kutch basin the western continental margin of india can be classed as a divergent or passive margin the western continental shelf is an extensive carbonate bank bombay offshore basin passing into clastic sediments on the north and south three craton margin embayed basins kutch cambay and narmada in the northern part of the shelf are filled predominantly with clastic sediments these basins occupy grabens bounded by faults diverging seaward the grabens were formed by three rift systems along major precambrian tectonic trends the rifting developed sequentially from north to south around the saurashtra horst kutch basin was formed in the early jurassic followed by cambay basin in early cretaceous time and the narmada in the late cretaceous it appears that these rifting ev nts occurred at successive stages during the northward migration of the indian plate after its break from gondwanaland in late triassic or early jurassic it is inferred that these rift basins opened up successively as a result of the counterclockwise drift of the indian craton bombay offshore and cambay are two major oil producing basins in the western margin these basins are characterized by high geothermal gradients attributed to the shallowness of the mantle in this region oil has not been found in kutch basin which is mainly an onshore mesozoic basin the basin depocenter shifted offshore at the northwestern part of the continental shelf where the shelf is wide

experimental modeling of pressurized subglacial water flow implications for tunnel valley formation tunnel valleys are elongated hollows commonly found in formerly glaciated areas and interpreted as resulting from subglacial meltwater erosion beneath ice sheets over the past two decades the number of studies of terrestrial tunnel valleys has continuously increased and their existence has been hypothesized also on mars but their formation mechanisms remain poorly understood we introduce here an innovative experimental approach to examine erosion by circulation of pressurized meltwater within the substratum and at the silicon substratum interface we used a permeable substratum sand partially covered by a viscous impermeable and transparent lid silicon putty below which we applied a central injection of pure water low water pressures led to groundwater circulation in the substratum only while water pressures exceeding the sum of the glaciostatic and lithostatic pressures led to additional water circulation and formation of drainage landforms at the cap substratum interface the formation of these drainage landforms was monitored through time and their shapes were analyzed from digital elevation model obtained by stereo photogrammetry the experimental landforms include valleys that are similar to natural tunnel valleys in their spatial organization and in a number of diagnostic morphological criteria such as undulating longitudinal profiles and tunnel shapes these results are consistent with the hypothesis that overpressurized subglacial water circulation controls the formation of tunnel valleys

middle late pleistocene landscape evolution of the dover strait inferred from buried and submerged erosional landforms abstract prominent landforms either buried or preserved at the seafloor provide important constraints on the processes that led to the opening and present day configuration of the dover strait here we extend previous investigations on two distinct landform features the fosse dangeard and lobourg channel to better understand the poly phase history of their formation and inferences for the opening and pleistocene evolution of the dover strait the fosse dangeard consist of several interconnected palaeo depressions their morphology and spatial distribution are interpreted to be the result of plunge pool erosion generated at the base of north eastward retreating waterfalls their infills comprise internal erosional surfaces that provide evidence for the occurrence of several erosional episodes following their initial incision the lobourg channel comprises various sets of erosional features attesting to the occurrence of several phases of intense fluvial and or flood erosion the last one of these carved a prominent inner channel which truncates the uppermost infill of the fosse dangeard the morphology of the lobourg inner channel and the erosional features associated with its incision strongly resemble landforms found in megaflood eroded terrains indicating that this valley was likely eroded by one or several megafloods our study therefore corroborates the existence of waterfalls in the dover strait at least once during the pleistocene epoch it also provides evidence of the occurrence of multiple episodes of fluvial and flood erosion including megafloods finally this study allows us to establish a relative chronology of the erosional depositional episodes that resulted in the present day morphology of this region

early eocene carbonaceous shales of tadkeshwar formation cambay basin gujarat india geochemical implications petrogenesis and tectonics abstract we report the early eocene cambay sedimentation petrogenesis and tectonics of a rift graben basin of western india using geochemistry the carbonaceous shales of tadkeshwar formation from tadkeshawar and rajpardi lignite mines of cambay basin were studied using major trace and rare earth elements the study reveals that the protolith of these shales is likely to be mafic to ultramafic in nature based on the high abundance of fe2o3 avg of 8 68 mgo avg of 5 78 and tio2 avg of 8 80 with a lower sio2 content avg of 44 74 when compared to paas values paas normalized ree distribution patterns of carbonaceous shales indicate relatively depleted lree with enriched hree coupled with small magnitude of eu eu strongly supports the protolith of these shales to be mafic to ultramafic weathering indices confirm these shales were derived from a source subjected to intense weathering low na2o and high perseverance of al2o3 are proxies for smectite to illite transformations of shales in a gaining temperature regime across the basin we speculate that the high geothermal gradients prevailed during 60 65 ma along the western margin of indian plate might be responsible for the intense weathering of the marine mafic protolith redox sensitive trace element ratios and negative ce anomalies suggest that the shales were deposited under suboxic to oxic environment the link between early eocene marine transgression followed by basin subsidence is inferred for the deposition of these carbonaceous shales in suboxic to oxic environments the immobile trace element ratios and geochemical discrimination diagrams k2o na2o vs si2o la th sc reveals the protoliths of the tadkeshwar formation were derived from a transitional domain of intra ocean island arc to active continental margin followed by convergence leading to the deposition of immature shales

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

a groove ploughing theory for the production of mega scale glacial lineations and implications for ice stream mechanics mega scale glacial lineations msgls are longitudinally aligned corrugations ridge groove structures 6 100 km long in sediment produced subglacially they are indicators of fast flow and a common signature of ice stream beds we develop a qualitative theory that accounts for their formation and use numerical modelling and observations of ice stream beds to provide supporting evidence ice in contact with a rough scale of 10 10 3 m bedrock surface will mimic the form of the bed because of flow acceleration and convergence in ice stream onset zones the ice base roughness elements experience transverse strain transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards where such keels slide across a soft sedimentary bed they plough through the sediments carving elongate grooves and deforming material up into intervening ridges this explains msgls and has important implications for ice stream mechanics groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream keels may provide basal drag in the force budget of ice streams thereby playing a role in flow regulation and stability we speculate that groove ploughing permits significant ice stream widening thus facilitating high magnitude ice discharge

provenance of eocene graywackes of the flournoy formation near agness oregon a geochemjcal approach systematic variations in major elements u and th contents and sr isotope ratios in graywackes of the flournoy formation near agness oregon are interpreted to indicate a multilithologic provenance at the time of deposition rb sr systems in the graywackes defined a pseudo isochron corresponding to an age of 110 m y calculated 87 sr 86 sr ratios range from 0 7050 to 0 7074 and compositional variations relate to these values in simple mixing patterns rb u th and k 2 o show a positive correlation with increasing 87 sr 86 sr o and decreasing mgo cao and sr average values of rb sr and 87 sr 86 sr at 50 m y ago for mesozoic graywackes otter point dothan galice and colebrooke formations are coincident with the mixing line defined by the rb sr systems of the flournoy graywackes suggesting that some combination of the mesozoic graywackes comprised part of the felsic component of the source terrane a mafic source is also required by chemical isotopic and mineralogic features of the flournoy graywackes this was probably equivalent to basalts in the paleocene and eocene roseburg formation beneath the flournoy

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

erosional origin of hummocky terrain in south central alberta canada we propose that hummocky terrain in south central alberta is the product of subglacial erosion rather than supraglacial letdown during ice disintegration a common view of hummock formation extensive exposures in hummocks contain sediments marking the history of laurentide ice advance and deglaciation in the region regardless of the genesis of those sediments units are abruptly truncated at the surface that represents the hummock and trough morphology indicating that the hummocks are the product of differential erosion subglacial sediments predating the erosion and subglacial eskers overlying the erosion surface suggest that the erosion was also subglacial hummock morphology lithostratigraphy correlated from hummock to hummock truncation at the land surface and widespread coarse boulder lags support a glaciofluvial origin for hummocky terrain in this region

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

genesis of the glacial curvilineation landscape by meltwater processes under the former scandinavian ice sheet poland abstract dobrzyn plateau in central poland contains a suite of enigmatic glacial bedforms termed glacial curvilineations gcl these landforms occur within tunnel valleys forming a complex anabranched network gcl consist of a series of parallel ridges extending for as much as 5 km over their length gcl ridges are parallel to neighboring ridges and to tunnel valley margins internal gcl composition consists of sand gravel and till distributed randomly within ridges and in intervening troughs electric resistivity tomography surveys confirm the sediment distribution seen in field exposures truncated beds near the ridge forms and the heterogeneous nature and distribution of sediments suggest an erosional rather than accretionary origin for gcl in this case internal gcl composition is not related to gcl genesis it records proglacial and subglacial conditions prior to gcl shaping by erosion the terminal zone of the anabranched tunnel valley network is characterized by a broad apron like ice marginal sedimentary complex sand and gravel dominate sedimentary facies within this zone sediments record evidence of meltwater sedimentation associated with supraglacial melting near the ice margin and high energy subglacial outbursts emanating from tunnel valleys this interpretation suggests that the gcl surface is a regional unconformity representing an erosional landscape where sediments within landforms offer limited insights into landform genesis cf sharpe et al 2004 subglacial meltwater erosion is proposed as unifying model of landscape development as it accounts for both erosion of tunnel valleys and gcl and meltwater dominated sedimentation in the ice marginal sedimentary complex

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

defending and testing hypotheses a response to john shaw s paper in defence of the meltwater megaflood hypothesis for the formation of subglacial bedform fields

late wisconsin subglacial megaflood paths in alberta evidence of late wisconsin subglacial megafloods includes fields of giant flutings drumlins tunnel channels and scoured bedrock tracts scoured tracts are marked by channeled scabland water eroded depressions s forms and postglacial development of solonetzic saline clay pan soils on cretaceous bedrock belts of hummocky terrain and small zones of moraine plateaus are remnants left by incomplete sheet flood erosion of initial subglacial sediment later modified by ice pressing among multiple subglacial discharges the largest was the livingstone lake event which transmitted laurentide water from the northwest territories and northern saskatchewan through alberta to montana and the mississippi drainage this flood was augmented by cordilleran water relayed under valley glacier piedmonts coalescent with south western laurentide ice the short duration megaflood probably occurred within the longer time interval of 18 15 ka

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

the athabasca fluting field alberta canada implications for the formation of large scale fluting erosional lineations abstract current drumlin and fluting hypotheses centred on processes of formation erosion and deposition by subglacial deformation accretion by lodgement glacial erosion and meltwater erosion and deposition rarely receive comprehensive field testing this paper documents the morphology internal structure and landscape associations of the athabasca fluting field alberta and discusses how well these characteristics are explained by postulated fluting forming processes fluting hypotheses are comprehensively tested by this approach and their rejection or acceptance are firmly based on field observation and knowledge of processes using multiple criteria fluting is shown to be erosional and not to be a product of pervasive subglacial deformation or accretion by lodgement morphology landscape associations bed truncation plus glaciofluvial lags and gravel on fluting ridges are inferred to support erosion by meltwater intact primary bedding synsedimentary faults and injection structures very close to the landsurface showing no sign of shear deformation are used to reject erosion by subglacial deformation fluting is shown to be closely associated with tunnel channels and indicates that these channels were overtopped by broad floods that formed the fluting field and eroded anabranching tracts over the length of the alberta plains prior to fluting formation sequences with melt out and lodgement till conduit sediment and boulder lags record net deposition over an extended time period diapirism prior to fluting formation marks a period of extreme pressure gradients which are related to bed separation following fluting formation there was only minimal landscape modification dominated by glaciofluvial and glaciolacustrine deposition not glacial processes this progression is presented as evidence for two very different glacial regimes separated by a short period with diapirism and extensive landscape modification by meltwater erosion we note that the study area was glaciated only once during the late wisconsinian and it follows that glacial sedimentation and landscape modification were confirmed to this single glacial episode

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

the subglacial geomorphology of southeast alberta evidence for subglacial meltwater erosion a coherent pattern of landforms in southeast alberta forms a subglacial landform continuum scoured bedrock tracts flutes transverse bed forms and tunnel channels in this continuum are inferred to be products of erosion by turbulent subglacial meltwater flows beneath the laurentide ice sheet bedrock and glacigenic sediment are truncated by an erosional surface flutes and extensive boulder lags across the truncation surface strongly suggest erosion by high velocity turbulent flows tunnel channels dissect the erosion surface and record channelization of earlier sheet flows convex longitudinal profiles of channels indicate subglacial meltwater flow northeast southwest trending transverse bed forms are superimposed on the preglacial divide and may be either glaciotectonic ridges or fluvial bed forms landforms reflect the dominance of erosion in the subglacial environment likely by catastrophic meltwater flows of the livingstone lake megaflood event the subglacial meltwater hypothesis accounts for e

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

laurentide subgiacial outburst floods landform evidence from digital elevation models various lines of landform evidence in many parts of canada are comprehensively explicable as products of subglacial sheetfloods outburst floods in the northwest territories northern saskatchewan and alberta landform associations such as scoured bedrock tracts cavity fill drumlins erosional drumlins erosional giant flutes remnant ridges tunnel channels channeled scabland and hummocky terrain with upstanding moraine plateaus reflect primary glaciofluvial erosional processes and secondary depositional activities the livingstone lake event major sheetfloods path arcs obliquely upslope from the keewatin district northwest territories through northern saskatchewan and much of alberta into montana u s a hill shaded maps generated from digital elevation models at widely varying scales are used to illustrate regional to local examples of megaflood landform suites complementary maps and diagrams are derived from more conventional data sources speculations regarding extraglacial implications of th

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

geochemistry and mineralogy of sediments from the ventersdorp and transvaal supergroups south africa cratonic evolution during the early proterozoic approximately 100 pelite and 12 quartzite samples from the ventersdorp 2 7 ga and transvaal supergroups 2 6 2 1 ga have been analyzed to monitor the early proterozoic evolution of the kaapvaal craton southern africa from oldest to youngest pelites were sampled from the ventersdorp bothaville bot transvaal selati sel black reef br timeball hill th strubenkop str and silverton sil formations paleocurrent measurements in transvaal quartzites indicate sources lying predominantly to the north and east relative to the bot sel br pelites from the th str sil are enriched in heavy ree lile zr hf nb and ta depleted in k2o mgo ni and cr and have lower cr zr sc th k2o na2o and k rb ratios compared to sel br bot th str sil pelites have higher light ree contents and la yb ratios and lower eu eu ratios 0 61 0 66 relative to nasc north american shale composite thstr sil pelites are enriched in light ree th u ta nb sc cs have higher la yb ratios and are depleted in k2o and mgo bot sel br pelites are enriched in k2o mgo cr and ni have higher k2o na2o sc th and eu eu ratios and are depleted in th u heavy ree and high field strength elements hfse relative to nasc compositions of th str sil pelites suggest a provenance similar to average phanerozoic uppercontinental crust this source is more evolved than that of bot sel br pelites indicating a transformation from primitive mafic rich to evolved felsic rich upper crust at 2 2 ga this transition follows earlier primitive to evolved trends in moodies pongola 3 3 3 0 ga and witwatersrand 2 8 ga successions these data suggest that several cycles of changing upper continental crust occurred in the kaapvaal craton between 3 3 2 1 ga

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

the blackspring ridge flute field south central alberta canada evidence for subglacial sheetflow erosion abstract the blackspring ridge bsr located in south central alberta canada is dominated by a prominent flute field flutes elongated streamlined depressions and ridges elongate streamlined hills are up to 15 km long and are composed of two material types in situ bedrock and in situ pre laurentide glaciation fluvial sand and gravel beds the preglacial beds are tertiary or early quaternary in age the beds are undisturbed maintain primary bedding structures and even maintain clast imbrication no till overlies the gravel beds although in places large granite boulder erratics lie on the surface indicating that ice was present in the region in the past because the ridges are composed of preglacial materials they are remnant erosional landforms rather than constructional landforms geomorphic and sedimentary evidence favor subglacial meltwater as the erosional agent rather than ice we suggest that the elevation of the bsr relative to basal ice would have resulted in confined subglacial meltwater flow with associated flow acceleration and increased scouring resulting in flute formation this meltwater stripped away any till cover leaving behind only a few boulders observations at the bsr flute field preclude the possibility that flutes and remnant ridges are the result of deformation of soft clayey beds

glaciofluvial erosional morphology and sediments of the coronation spondin scabland east central alberta spatially discontinuous meltwater channel networks on the canadian prairies are usually interpreted as having formed subaerially in front of the retreating laurentide ice sheet evidence in the coronation spondin scabland east central alberta supports an alternative formation by progressive channelization of a subglacial sheetflow of water the scabland is an integrated channel network with varying degrees of anabranching the channels having highly variable sizes shapes and orientations enhanced scour at some channel confluences reflects contemporaneous channel utilization channels also display convex up concave up and undulatory along channel profiles with some junctions at the same elevations longitudinal grooves in large scale channels are associated with numerous boulder deposits residual hills demarcated by channels display composite and streamlined forms superimposed on residuals are erosional transverse bedforms longitudinal grooves and undulating surfaces that indicate submergence

in defence of the meltwater megaflood hypothesis for the formation of subglacial bedform fields characteristics of large scalefluting and hummocky terrain on the canadian prairies test glacial and meltwater hypotheses for landform genesis these tests defend the meltwater model neither sedimentary nor glaciotectonic processes can fully explain such erosional landforms province scale flow paths which mark palaeo ice streams and subglacial flood routes contain large scale fluting with flanking hummock terrain antecedent relief causes these paths to differ from other flood landscapes such as the scablands proponents of the glacial hypothesis use an invalid analogy between icelandic and prairie landsystems they suggest that groove ploughing formed large scale fluting and that ice pushing created hummocky terrain however landform location form and extent surface lags truncated architecture and landform associations favour the meltwater hypoth esis a simple thought experiment and clear understanding of the principle of least number of assumptions answer the criticisms that meltwater forms cannot cross cut and that the meltwater hypothesis disregards proper hypothesis testing an example of cross cutting erosional marks supports this theory no narrow tract of smoothed terrain with fluting terminates at the glacially thrust neutral hills negating an important point in the glacial hypothesis while neither the glacial hypothesis nor postglacial winnowing explain boulder and cobble lags with percussion marks meltwater processes explain them well copyright 2009 john wiley sons ltd

the controls on the major and trace element variation of shales siltstones and sandstones of pennsylvanian permian age from uplifted continental blocks in colorado to platform sediment in kansas usa shales siltstones and sandstones of pennsylvanian permian age from near the source in colorado to those in the platform in eastern colorado and kansas have been analyzed for major elements and a number of trace elements including the rees the near source sandstones are significantly more enriched student t test at better than the 99 confidence level in sio2 and na2o concentrations and more depleted in al2o3 fe2o3 total tio2 th hf sc cr cs rees y and ni concentrations and laco and lani ratios than the near source shales and siltstones most likely due to more plagioclase and quartz and less clay minerals in the sandstones than in the shales and siltstones there are no significant differences in k2o and sr concentrations and eueu lalu lase thsc thco and crth ratios between the near source sandstones and the near source shales and siltstones samples of the molas hermosa and cutler formations near the source that were formed in different environments in the same area contain no significant difference in eueu lalu lasc thsc thco and crth ratios so a generally silicic source and not the environment of deposition was most important in producing these elemental ratios for example crth ratios of near source shales siltstones and sandstones range from 2 5 to 17 5 and eueu range from 0 48 to 0 78 which are in the range of sources of sediments derived from mainly silicic and not basic sources near source shales and siltstones contain significantly higher student t test and more varied concentrations of most elements al2o3 fe2o3 mno tio2 ba th hf ta co sc rees nb y but significantly lower concentrations of na2o and eueu than platform shales and siltstones in kansas e g la 65 7 40 and eueu 0 55 0 07 in near source shales and siltstones and la 23 7 8 7 and eueu 0 64 0 08 in platform shales and siltstones the sio2 and cao concentrations are not significantly different in platform shales and siltstones compared to the near source shales and siltstones so dilution of other minerals by quartz and calcite is not the main reason for the lower concentration of most elements in the platform relative to the near source shales and siltstones rather the lesser concentrations of most elements in clay minerals of the platform shales and siltstones can account for the lower concentration of most elements compared to corresponding near source shales and siltstones the lower concentrations of many elements in clay minerals in the platform shales and siltstones may be a result of having been derived from recycling of clay minerals from older rocks the greater homogeneity of elemental concentrations of the platform shales and siltstones compared to those in the source is also consistent with homogeneous mixing of such recycled material also there is no significant difference in thsc laco thco lani and crth ratios of the near source sedimentary rocks in colorado to the platform shales and siltstones in kansas and the latter are also consistent with derivation from mostly silicic source rocks

trace and rare earth elemental variation in arabian sea sediments through a transect across the oxygen minimum zone we have determined the calcium carbonate caco3 organic carbon coorg trace element and rare earth element ree composition of surface sediments collected from a transect on the central western continental shelf and slope of india in the eastern arabian sea the transect samples across the oxygen minimum zone omz allows us to compare the relative abundances of trace elements and rees in the sediments beneath and beyond the omz shale normalized ree patterns lan ybn ratios and eu eu anamolies indicate that the sediments in the study area are either derived from the adjoining archaean land masses or from distal indus source sediment deposited in the omz have high u values from 3 6 to 8 1 ppm with their uexcess of that can be supplied by continental particles values ranging between 82 91 of the total u indicating that the u may be precipitated as u 4 in the reducing conditions of omz sediments deposited beneath the intense omz 0 2 ml l and away from the omz 1 2 ml l show slight negative ce anomalies with no significant differences between these two sets of sediments the ce ceshale values are poorly related to u and corg which are indicators of suboxic bottom waters normative calculations suggest that two sources namely terrestrial and seawater terrestrial seawater contribute to the total cc anomaly of the sediments the cc anomaly values of the calculated seawater derived component are similar to the anomalies reported for other coastal waters and the oxygenated surface waters of the arabian sea and do not show any correspondence to the lowered redox state of the overlying water probably due to the redirection of dissolved ce into the oxic deeper water this data on recently deposited sediments from a known oxygen poor environment suggest that the ce cesh in high sedimentation areas of continental margin environments may not be a good paleoredox proxy u th ratios above 1 25 noticed in omz are in accordance with the earlier usage of this ratio for identifying reducing environment of ancient sediments

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

ice thrust terrains and glaciotectonic settings in central alberta airphoto analyses geologic field mapping and study of borehole logs and surficial topographic maps in ice thrust terrains in central alberta suggest that all these techniques are needed to identify ice thrust terrains that may or may not have topographic expressions three geomorphological settings susceptible to glaciotectonic deformation are described as escarpment valley and plains settings the bedrock slopes in the escarpment setting ranged from 19 to 51 m km the bedrock slopes in the valley setting ranged from 23 to 32 m km and the valley was 8 5 km wide between crests and 4 km at the bottom the bedrock slopes of the plains setting ranged from 2 to 5 m km ice thrust features are found in topographic troughs in front of an ice sheet where water bodies were impounded these proglacial water bodies thawed the permafrost in front of the glacier the disintegration of proglacial permafrost decreased the resistance of subglacial strata to ice thrusting ice thrust features can be expected in areas wh

wet subglacial bedforms of the ne greenland ice stream shear margins we describe elongate wet subglacial bedforms in the shear margins of the ne greenland ice stream and place some constraints on their formation lateral shear margin moraines have been observed across the previously glaciated landscape but little is known about the ice flow conditions necessary to form these bedforms here we describe in situ sediment bedforms under the ne greenland ice stream shear margins that are observed in active source seismic and ground penetrating radar surveys we find bedforms in the shear margins that are 500 m wide 50 m tall and elongated nearly parallel to ice flow including what we believe to be the first subglacial observation of a shear margin moraine acoustic impedance analysis of the bedforms shows that they are composed of unconsolidated deformable water saturated till we use these geophysical observations to place constraints on the possible formation mechanism of these subglacial features

a ploughing model for the origin of weak tills beneath ice streams a qualitative treatment abstract glaciological studies of west antarctic ice streams have shown that weak sub ice stream tills provide the basal lubrication that makes fast ice streaming possible under low driving stresses given the significant current interest in time dependent ice stream behavior there is a clear need for a conceptual model of weak sub ice stream tills that treats in a simple but physically correct way the coupling between evolution of till properties and ice stream dynamics as a possible alternative to the previous viscous bed model we propose a ploughing model that is consistent with the experimentally determined coulomb plastic rheology of sub ice stream till in the ploughing model the till is a several meters thick layer of sedimentary material that is disturbed and transported by ploughing that occurs during sliding of a bumpy ice base the thickness of the till layer is determined in the ploughing model by the amplitude of the largest roughness elements ice keels there is no direct proof for the existence of ice bumps and ice keels beneath the modern west antarctic ice streams but bedforms e g megalineations and bundle structures left behind by pleistocene ice streams strongly support our assumption that an ice stream base is irregular generation of new till material occurs when ice keels protrude through the existing till layer and erode the top of the sub till preglacial sediments based on a single tethered stake measurement of engelhardt and kamb j glaciol 44 1998 223 made at the upb camp ice stream b west antarctica fig 1 we estimate that the till flux due to sliding with ploughing is there 3 yr 1 per meter width to balance the estimated till flux in the upb area substrata erosion by ice keels would have to take place at a high but not unreasonable non dimensional rate of 4 assuming 1 contact area in the case of the west antarctic ice streams erosion of sub till materials by ice keels may be particularly fast and unimpeded because these ice streams are overriding unlithified preglacial tertiary sediments the most significant implication of the proposed ploughing model is that it permits treating basal resistance to ice motion as being velocity independent plastic till rheology while allowing subglacial transport of till as in the viscous bed model models of ice streams with a plastic bed exhibit a greater potential for unstable behavior than models of ice streams with viscous beds

incipient tunnel channels abstract glaciated terrains in east central alberta and south central michigan contain channels that have hummocks and transverse ridges separating depressions along their floors this association imparts a linked pothole appearance similar channels are often interpreted as tunnel channels or subaerial channels partly filled with sediment from a subsequent glacial advance a stagnating ice roof or slumped sediment from the channel margins however the truncation of sedimentary packages in the channel walls and intrachannel hummocks indicates that they are erosional landforms cut into glacial sediments till bedrock or gravel eskers overlie and are found within a few channels indicating that these channels formed before the final stagnation that produced the eskers these two characteristics combined with the observation that many channels have convex up long profiles indicate that the channels were eroded by pressurized subglacial water because the formative mechanisms for this type of channel are not clear and modern environments that could produce this type of landform are inaccessible we draw on several morphologic analogues to propose mechanisms for channel erosion we conclude that the erosion of these linked pothole channels incipient tunnel channels was the product of the complex interaction between complex turbulent flow structures and various scales of roughness elements

short paper ophiolitic detritus in the ordovician sediments of south mayo ireland sandstones from ordovician sediments of the south mayo trough western irish caledonides show marked stratigraphic variation in their major and trace element geochemistry high cr ni and mg concentrations of ultramafic derivation succeed high ti and fe concentrations of mafic provenance this sequence is interpreted as the result of the progressive unroofing of an ophiolite a possible sedimentary linkage with ophiolite lithologies in the clew bay domain to the north would indicate minimal post arenig transcurrent displacement the south mayo flysch with its ophiolitic detritus is typical of caledonian flysch sequences which pre date the mid ordovician taconic deformation but differs in character from those of late ordovician age

geotechnical model for great plains hummocky moraine formed by till deformation below stagnant ice abstract hummocky or disintegration moraine is a widespread late wisconsin glacial terrain type across the glaciated great plains of mid continent north america this terrain consists of chaotic hummocks and enclosed kettle hollows that are widely underlain by clay rich till the prevailing interpretation of this terrain is one of supraglacial deposition from debris covered stagnant ice and is based largely on geomorphologic comparisons with modern valley glacier margins recently in contrast it has been argued that hummocky moraine can form subglacially by the pressing of fine grained deformable till under the overburden pressure of stagnant ice in this paper we test the postulated subglacial origin of hummocky moraine using a geotechnical model of a deforming soil till the model confirms that hummocky topography can be the result of failure and deformation of fine grained till by differential loading below stagnant ice differential pressures at the ice bed contact arise from the complete or partial perforation of thin stagnant ice sheet lobes by numerous water filled doline like depressions the growth and decay of ponds as ice down wastes result in repeated cycles of subglacial till failure and landform development resulting in the observed random linear circular elongate and other patterns of hummocks ridges and hollows formerly streamlined preferentially oriented subglacial landforms such as drumlins and rogen moraines can also be overprinted forming washboard moraine

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

the controls on the major and trace element evolution of shales siltstones and sandstones of ordovician to tertiary age in the wet mountains region colorado u s a a vertical section of shales siltstones and sandstones from ordovician to eocene age in a limited geographic area east of the wet mountains and sangre de cristo mountains in colorado have been analyzed for major elements and a variety of trace element concentrations including the ree in addition the petrography of the sandstones has been determined the quartz rich arenites contain considerably lower concentrations of most elements relative to coexisting shales or siltstones at the same outcrop the arkosic sandstones contain similar to lower concentrations of most elements compared to coexisting shales or siltstones in the same area accordingly the average concentrations of al2o3 fe2o3 mgo tio2 loi rb th co sc cr cs nb y and ree are significantly lower in all sandstones relative to all shales and siltstones the exceptions are sio2 na2o and ba concentrations and the eu eu lasc and thsc ratios as they are higher in the sandstones than the shales and siltstones there is no significant difference in the mno cao k2o and sr concentrations or the sollaco thco lani crth and lalucn ratios of the average sandstones relative to the shales and siltstones many of these differences may be related to the higher quartz and feldspar and lower clay mineral amounts in the sandstones than in the shales and siltstones for example average lasc thsc eueu and lalucn ratios of th arkosic sandstones tend to be higher than the coexisting shales and siltstones due to enrichment of the arkoses in feldspar relative to the other minerals e g eueu 0 82 0 19 in average arkoses in the trinidad vermejo raton poison canyon and cuchara formations eueu 0 63 0 19 in average shales and siltstones in the same formations in addition the elemental concentrations and ratios are more variable for most elements in the sandstones than the shales and siltstones this suggests that the shales are rapidly homogenized near the source the elemental fractionation in the arkosic sandstones due to enrichment of feldspar relative to other minerals suggests that they are poorer indicators of provenance that the associated shales whereas the more homogeneous elemental distributions in the shales and siltstones suggest that they may be better indicators of provenance than the sandstones nevertheless the elemental ratios that are most similar in the sandstones and in the shales and siltstones are consistent with their derivation from similar average intermediate to silicic source rocks

reply defending and testing hypotheses a response to john shaw s paper in defence of the meltwater megaflood hypothesis for the formation of subglacial bedform fields

implications of elemental concentrations for provenance redox conditions and metamorphic studies of shales and limestones near pueblo co usa abstract major element and some trace element compositions including the ree of shales carbonate rich shales and limestones of late cretaceous age have been analyzed at two outcrops near pueblo co elemental ratios that are characteristic of the provenance of terrigenous debris that are the least variable with changing percent acid insoluble residue vs percent calcite are th cr la co la lu cn and eu eu the ce ce la sc and la cr ratios however are only constant when greater than 30 of a sample is composed of acid insoluble residue at less than 30 acid insoluble residue these elemental ratios increase markedly the th co and th sc ratios are fairly constant from nearly 0 to about 60 acid insoluble residue above 60 residue these ratios increase due to the high concentration of th in the graneros to hartland shales at everhart ranch the average of the th co th sc th cr la co la sc and la cr ratios are similar to those of the mcs mid continent shales and paas post archean australian shales thus these carbonate rich to carbonate poor rocks analyzed in this study contain terrigenous debris that has been derived from granitoids similar to those that supplied debris to the mcs and paas the ce ce ratios are lower and the mn mn log mn sample mn shales fe sample fe shales values are more positive in the more calcite rich bridge creek and ft hays limestones than in the other units suggesting that they formed in an oxidizing environment the ce ce are the highest and the mn values are the most negative in the graneros to hartland shales suggesting that they formed under more reducing conditions the elemental concentration of one sample relative to that of another sample over a few meters distance usually vary in small amounts e g medians of the ratios of the same elements between adjacent samples ranges from 1 06 to 1 70 however the ratio of elemental concentrations between adjacent samples can sometimes be quite large the least variation of elemental ratios between adjacent samples often occurs within the more carbonate poor shales the greatest variation occurs within the limestones thus trying to decipher local movement of elements due to metamorphism in similar carbonate shale limestone sequences should be done cautiously since local elemental variation due to sedimentary processes can be large

ice walled lake plains implications for the origin of hummocky glacial topography in middle north america abstract ice walled lake plains are prominent in many areas of hummocky till topography left behind as the laurentide ice sheet melted from middle north america the formation of the hummocky till topography has been explained by 1 erosion by subglacial floods 2 squeezing of subglacial till up into holes in stagnant glacial ice or 3 slumping of supraglacial till the geomorphology and stratigraphy of ice walled lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin these flat lake plains up to a few kilometers in diameter are perched as much as a few tens of meters above surrounding depressions they typically are underlain by laminated fine grained suspended load lake sediment many ice walled lake plains are surrounded by a low rim ridge of coarser grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes the ice walled lakes persisted for hundreds to thousands of years following glacial stagnation shells of aquatic molluscs from several deposits of ice walled lake sediment in south central north dakota have been dated from about 13 500 to 10 500 b p calibrated radiocarbon ages indicating a climate only slightly cooler than present this is confirmed by recent palaeoecological studies in nearby non glacial sites to survive so long the stagnant glacial ice had to be well insulated by a thick cover of supraglacial sediment and the associated till hummocks must be composed primarily of collapsed supraglacial till

does porewater or meltwater control tunnel valley genesis case studies from the hirnantian of morocco several ordovician tunnel valleys are exposed in the moroccan anti atlas mountains including the alnif and the foum larjamme tunnel valleys located 150 km away from each other sedimentological and deformational analyses of these two glacial troughs reveal that differing processes lead to their formations the alnif tunnel valley contains numerous deformation structures within sediments both below and above the main glacial erosion contact surface ball structures and clastic dykes occur within preglacial sediments down to 35 m below glacial incisions while overlying glacial sediments contain fluted surfaces clastic dykes dewatering structures folds and radial step normal faults the characteristics of the alnif tunnel valley can be explained by a porewater pressure driven model of formation where the localized increase of basal shear stress and porewater pressure underneath subglacial deforming zones lead to the development of a dense hydrofracture network in the preglacial bed these processes of hydraulic brecciation promoted subglacial remobilization of the preglacial material and contributed to the formation of the tunnel valley the foum larjamme tunnel valley displays undisturbed preglacial sediments and few dewatering structures at the base of the glacial sedimentary infill which suggests relatively low porewater pressures within the tunnel valley during formation this second type of tunnel valley where porewater pressure remained relatively low appears to have been formed by meltwater erosion the undulating base of the foum larjamme tunnel valley implies progressive erosion by a stable subglacial braided network of nye channels or alternatively by channels migrating laterally during episodic minor subglacial outbursts these two tunnel valleys highlight the regional variability of processes involved in the formation of tunnel valleys the distribution of palaeo ice streams in north africa illustrate that morphologies and processes involved in the formation of tunnel valleys vary between ice stream and inter ice stream zones due to variations in meltwater availability the topography and bed lithological properties

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd