hummocky cross stratification and megaripples a geological double standard abstract hummocky cross stratification in ancient sedimentary deposits is considered to be diagnostic of inner shelf storm deposits the geometry of the cross strata sets implies a low relief oval bedform of a few meters spacing orientation is poorly defined or random hummocky cross strata sets have been attributed to the action of strong storm wave surges megaripples of 2 5 m spacing are typical responses of the inner atlantic shelf of north america to storm flows side scan sonar records have shown that megaripples on the inner shelf are commonly hummocky oval to circular in plan view and lack asymmetry box cores and vibracores reveal gently inclined to horizontal lamination as the characteristic primary structure the megaripples am produced by combined flow storm currents these are alongcoast geostrophic flows with a mean flow component of 20 60 cm sec 1 a high frequency wave orbital current of similar or weaker intensity is present but its role in megaripple formation is subordinate to that of the mean flow the high velocity coastal margin of the flow is often jetlike and downwelling in nature and is characterize by a down current decrease in sand flux and rapid deposition of sand the bottom boundary layer of such flows is characterized by dense sediment suspensions 40 60 mgl 1 and is highly turbulent due to the interaction of the mean flow and wave orbital current components eddy diffusivity up to 200 cm2 sect at 40 cm above the bed sand transport in this coastal boundary zone is obliquely offshore but neither the density of the sediment suspension nor storm surge ebb appear to be important driving forces it is difficult to account for either modern hummocky megaripples or ancient hummocky cross stratification as responses to purely oscillatory flows combined flow currents are the typical response of mostmodern shelves and epicontinental seas to storms and presumably were so in the past hummocky cross stratified beds are generally too thick 20 80 cm to be accounted for by in situ resuspension they are more likely to have been despoited by combined flow currents in areas where these currents were experiencing a downstream velocity decrease and sediment deposition throughout much of the storm s duration evidence for strong scour in swales between hummocks and the smoothly rounded surface of the hummocks suggests a transitionlike bed regime measurements on the atlantic shelf likewi e suggest a transitionlike regime whose boundary layer is characterized by lower velocity than the transitional regime of unidirectional flow in flumes but more intense turbulence and a higher suspended sand concentration the lack of normal cross bedding in bothmodern and ancient hummocky bedforms indicates that these features did not migrate this characteristic may be a consequence of the complex trajectories followed by near bottom water particles in response to combined flow currents

model for the combined flow origin of hummocky cross stratification many shallow marine sandstones are characterized by gently dipping trough cross stratification there appear to be significant similarities between this low angle cross stratification and typical hummocky cross stratification and it is proposed that much of what is currently recognized as hummocky cross stratification is related to low relief megaripple bed forms that are equilibrium structures for fine grained sand under combined wave surge and unidirectional currents the geometry that obtains when these bed forms migrate is low angle trough cross stratification high rates of sedimentation from incipient suspension and limited lateral migration of individual bed forms promote preservation of convex upward depositional surfaces hummocks between troughs highly unsteady flow leads to abundant internal scour and drape surfaces neither random scour and drape nor oscillatory currents seem sufficient to generate hummocky bed forms

hydraulic modelling of subglacial tunnel channels south east alberta canada one of the key issues associated with the hypothesis of catastrophic subglacial drainage of the livingstone lake event is whether flows of such large magnitudes are physically feasible to explore this issue a one dimensional hydraulic network flow model was developed to investigate the range of peak discharges and associated flow parameters that may have been carried by a tunnel channel network in south east alberta canada this tunnel channel network has been interpreted elsewhere to carry large discharges associated with subglacial meltwater flows because of the convex longitudinal profiles of individual channels this computational modelling effort draws upon established and verified engineering principles and methods in its application to the hydraulics of this problem consequently it represents a unique and independent approach to investigating the subglacial meltwater hypothesis based on the modelling results it was determined that energy losses resulting from friction limit the maximum peak discharge that can be transported through the tunnel channel network to 10 7 m 3 s 1 which is in reasonable agreement with previous estimates of flood discharges for proposed megafloods results show that flow through channels with convex longitudinal profiles occurs when hydraulic head exceeds 910 m lost river and 950 m sage creek respectively these are considerably below the maximum head capable of driving flow through the system of 1360 m beyond which ice is decoupled from the bed across the pre glacial drainage divide therefore it is concluded that these model results support the hypothesis of catastrophic subglacial drainage during the livingstone lake event

bedform genesis in bedrock substrates insights into formative processes from a new experimental approach and the importance of suspension dominated abrasion bedrock channels are common in the natural environment and bedrock channel erosion sets the pace of denudation in many river catchments however in comparison to the large number of studies concerning the formation of alluvial bedforms relatively few investigations have concerned bedrock bedform genesis field based analysis of sculptured forms within bedrock channels has been restricted notably by the slow rate of bedform development in such environments furthermore only a limited number of flume scale experiments have been conducted that attempt to simulate the genesis of sculpted bedforms in bedrock channels this study demonstrates that optimisation of clay beds through analysis of clay strength enables the development of features analogous to bedrock river channel bedforms even at a scale that is orders of magnitude smaller than some natural examples three sets of suspended sediment laden experiments were carried out using hard medium and soft clay bed substrates a suite of erosive bedforms including potholes flutes and furrows developed on all experimental beds all observed erosional features have clear equivalents to those observed in natural bedrock rivers bed shear strength was found to be a significant factor for the genesis of different types of simulated bedrock bedforms in our experiments with other factors such as flow velocity bed slope and flow depth held approximately constant importantly in a subset of experiments performed with an absence of suspended sediment fluid flow did not result in the erosion and development of bedforms in the clay bed hence this work illustrates that abrasion by suspended sediments is the key process required for the formation of these simulated bedrock bedforms in our experiments in the absence of bedload abrasion other processes such as plucking cavitation and dissolution will have been negligible

tunnel channels in southeast alberta canada evidence for catastrophic channelized drainage abstract tunnel channels in southeast alberta are attributed to erosion by channelized subglacial meltwater flows an anabranching tunnel channel network dissects the preglacial drainage divide of the ancestral milk river channel morphology and landform associations are used to evaluate competing hypotheses of tunnel channel formation mechanisms that invoke subaerial channel incision direct glacial erosion or steady state time transgressive erosion at the ice margin cannot explain convex up longitudinal channel profiles anabranching channel networks or confinement to the preglacial drainage divide results conclude that the tunnel channel network in southeast alberta represents late stage erosion by a channelised subglacial flow of catastrophic dimensions interpretations for this tunnel channel network are in agreement with conclusions obtained for the regional subglacial landform assemblage

the lemniscate loop comparisons with the shapes of streamlined landforms the lemniscate loop is a streamlined geometric form which has a simple algebraic equation containing a parameter whose value governs its overall length to width dimensions the lemniscate has been employed in geomorphology including comparisons with glacial drumlins and erosional streamlined islands in the channeled scabland of eastern washington and within the channels on mars these past comparisons have mainly been visual the present study involves more detailed quantitative comparisons between the lemniscate loop symmetrical airfoils drumlins and various islands formed by water flows the analyses focus primarily on the length to width ratios of these landscape features and their consistency with the analytical lemniscate shape many drumlins are found to be similar to the streamlined lemniscate but an equal number are more closely approximated by an elliptical geometric form the streamlined islands in rivers in the channeled scabland and in the martian channels all have nearly the same ave

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

origin of glacial fluvial landforms in the azas plateau volcanic field the tuva republic russia role of ice magma interaction the basaltic azas plateau volcanic field is located in the tuva republic of the russian federation the area was glaciated multiple times and the field is characterized by the formation of subglacial volcanoes called tuyas but subaerial volcanoes and lava fields also exist a combined study of remote sensing and field observations in the vicinity of the tuyas in the southeastern azas plateau volcanic field identified landforms that are best explained by the jokulhlaup hypothesis the landforms include elongated hills paleochannels and butte and basin topography these landforms are hypothesized to have formed by both erosion and deposition caused by high energy water streams the triggering for the hypothesized jokulhlaups was either melting of ice by subglacial volcanism and or destabilization of ice dammed subglacial reservoirs the age estimation of the flood events is difficult but they probably occurred during the ice ages of the quaternary as late as in the middle late pleistocene

discussion streamlined erosional residuals and drumlins in central british columbia canada by j donald mcclenagan 2013 geomorphology 189 41 54 abstract mcclenagan 2013 presents a model to explain streamlined erosional residuals or drumlins on uplands and lowlands in the plateau region of central british columbia canada in this discussion paper we note that mcclenagan 2013 has not adequately discussed previous relevant work in the region and we argue that additional analyses and evidence are required to substantiate this new model the hypothesis offered for the origin of the plateau landscape specifically catastrophic glaciofluvial activity differs significantly from a model based on glacial erosion and deformation that has been developed from field based research over the past six decades we discuss four critical points relating to the proposed model 1 the current geological model for the plateau region of central british columbia 2 theory of glacial dispersal 3 existing hypotheses for the formation of drumlins and other glacial landforms and 4 theoretical glacial erosion modeling we further suggest that the model cannot be substantiated without sedimentological or morphological field evidence for water bodies argued to be the source of the proposed megaflood or megafloods

40ar 39ar dating of latest pleistocene 41 ka marine tephra in the mediterranean sea implications for global climate records abstract fifty one 40 ar 39 ar laser heating analyses of sanidine crystals in the c 13 tephra layer recovered out of a piston core raised from 3000 m depth in the tyrrhenian sea yielded apparent ages between 25 and 112 ka twenty four of these measurements define an age probability maximum and generate an isochron of 41 1 2 1 ka 2 with a 40 ar 36 ar intercept of 288 21 that is indistinguishable from the modern atmosphere however the entire population is skewed toward older apparent ages with smaller peaks at 48 ka 55 ka 67 ka and 110 ka the composition of glass shards in the c 13 tephra overlaps that of the sio 2 rich phase of the 150 km 3 campanian ignimbrite which erupted from the campi flegrei caldera 130 km northwest of the core site although the 41 1 2 1 ka isochron is 15 older than k ar and 14 c ages for the campanian ignimbrite it is indistinguishable from recent 40 ar 39 ar age determinations the campanian ignimbrite eruptions were also chemically similar to and correlated with the y 5 ash layer the most voluminous and widely dispersed late pleistocene tephra in the mediterranean region the age of the y 5 layer was constrained originally at 38 0 2 5 ka on the basis of astronomical dating of o isotope stages the 40 ar 39 ar ages astronomical dating plus chemical similarities permit correlation of the c 13 tephra layer with both the campanian ignimbrite and the y 5 tephra layer the older ages preserved in the c 13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the campi flegrei caldera 41 ka the c 13 tephra layer is correlated with a 10 be peak in an adjacent marine core o isotope stage 3 12 and immediately preceded a cooling episode corresponding to heinrich event 4 thus the age of these features is constrained by radioisotope dating the 41 ka peak in 10 be deposition is a global phenomenon whose age matches that of the laschamp geomagnetic excursion thus our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr precise age information independent of radiocarbon dating can be recovered from latest pleistocene marine tephra using the 40 ar 39 ar laser heating method despite the presence of multiple components that may have been incorporated during or after its deposition

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

cardium formation u cretaceous at seebe alberta storm transported sandstones and conglomerates in shallow marine depositional environments below fair weather wave base as a result of detailed mapping at seebe alberta we have defined five coarsening upward sequences in the turanian cardium formation the sequences begin with bioturbated mudstones and coarsen int

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

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

a depositional model for rogen moraine with examples from the avalon peninsula newfoundland rogen moraine is explained by subglacial meltwater processes through a form analogy between moraine ridges and ripples produced on the underside of river ice this mechanism for rogen moraine formation is compatible with the meltwater hypothesis for drumlins a unified explanation for rogen moraines and drumlins is attractive and necessary because they are part of a continuum the meltwater hypothesis is tested on rogen moraine of the avalon peninsula newfoundland mapping shows that ice and meltwater flowed northeastwards from st mary s bay and fanned out across the peninsula the sedimentology of four moraine ridges and one moraine hummock favours deposition in subglacial cavities sediment in the ridges travelled only short distances and there is abundant evidence of water sorting and deposition from debris flows bedding within ridges conforms with surface slopes and clast fabrics relate to local morphology rather than to the regional ice flow direction additional sedimentary observations from qu

sedimentary response to mississippian tectonic activity at the east end of the 38th parallel fracture zone carbonate fades of the greenbrier group establish the presence of an east west trending mississippian uplift and record the timing of late paleozoic tectonic movement in the east central appalachian basin at the east end of the 38th parallel fracture zone this fracture zone has been defined by previous workers from the alignment of igneous intrusive and volcanic rocks ore mineralization zones major fault systems and landsat lineaments across eastern and central north america this fracture system is apparently associated with displacement along faults in the precambrian basement rock movement along the fracture zone occurred periodically throughout the phanerozoic the lineament may be distinguished both geomorphically on landsat imagery and side looking airborne radar and stratigraphically mississippian tectonic activity along the eastern section of the fracture zone is indicated by anomalous thinning of sediments facies patterns and stratigraphic relations of uppermost devonian to upper mississippian strata of the eastern appalachian plateau

incised valley fill interpretation for mississippian black hand sandstone appalachian basin usa implications for glacial eustasy at kinderhookian osagean tn2 tn3 boundary abstract lower mississippian strata of east central ohio are predominantly fine grained marine deposits of the cuyahoga and logan formations within these sediments is the black hand sandstone of the cuyahoga formation the black hand sandstone is a multistory crossbedded coarse grained conglomeratic sandstone the contact between the black hand sandstone and the subjacent cuyahoga formation is sharp and scoured with intraclasts of the cuyahoga formation incorporated into the basal black hand sandstone the black hand sandstone was previously thought to represent a distributary channel deposit however the combination of lithofacies and architectural elements indicates deposition in a braided stream setting the cuyahoga formation was deposited in a shallow marine setting the erosional basal contact of the black hand sandstone and the juxtaposition of fluvial and marine sediments suggests a sequence boundary the geographic distribution of the black hand sandstone combined with the evidence for a sequence boundary suggests deposition in an incised valley the age of the black hand sandstone is key to inferring the causes of valley incision the black hand sandstone is nearly devoid of body fossils necessitating a biostratigraphic analysis of the surrounding cuyahoga and logan formations analysis indicates the logan formation is early osagean age data from the cuyahoga formation suggest a kinderhookian age with a possible transition to the osagean in the uppermost cuyahoga formation this constrains the age of the black hand sandstone to the transition at the kinderhookian osagean boundary recent reports indicate late kinderhookian tournaisian tn2 gondwanan glaciation based upon tillites and sharp excursions in stable isotope curves a glacio eustatic fall in sea level is inferred to have caused incision of the cuyahoga formation followed by deposition of the black hand sandstone and logan formation during the subsequent sea level rise the associated unconformity correlates to the sequence boundary at the kinderhookian osagean boundary in the stratotype area of north america and the correlative tn2 tn3 boundary worldwide supporting the hypothesis of a global eustatic event at this time

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

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

hydrographic conditions of the devono carboniferous north american seaway inferred from sedimentary mo toc relationships abstract deepwater anoxia developed widely within a series of silled intracratonic basins in north america during the middle devonian to early carboniferous but the hydrographic factors contributing to this development are virtually unknown the present study demonstrates that the degree of enrichment of strongly hydrogenous elements such as molybdenum mo in the organic rich shales that accumulated in these basins has the potential to provide information about paleohydrographic conditions most of the study units 49 of 55 exhibit significant positive covariation between elemental mo and toc concentrations yet there is substantial variation in the statistical parameters that define these relationships specifically the regression lines characterizing mo toc covariation have slopes m ranging from 2 to 65 10 4 although a majority of the study units yield m values between 10 and 25 10 4 the parameter m exhibits systematic stratigraphic variation within individual basins and geographic variation among basins suggesting that mo toc relationships were controlled by slowly evolving watermass characteristics of the devono carboniferous north american seaway a recent study of modern anoxic silled basins algeo t j lyons t w 2006 mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions paleoceanography 21 pa1016 doi 10 1029 2004pa001112 demonstrated that m is closely linked to the degree of restriction of the subpycnoclinal watermass as reflected in aqueous mo concentrations mo aq and deepwater renewal times dw these relationships reflect control of sedimentary mo enrichment by both the amount of sedimentary organic matter i e host phase availability and the concentration of aqueous mo i e source ion availability when applied to black shales of the devono carboniferous north american seaway these relationships permit both qualitative and quantitative inferences regarding the degree of restriction of deepwaters in cratonic basins and the evolution of hydrographic conditions through time black shales associated with early stages of sea level rise commonly exhibit low m values 1000 yr higher sea level stands resulted in more open marine conditions and enhanced deepwater renewal leading to deposition of black shales with m values up to 65 equivalent to mo aq 70 of the normal seawater concentration and dw

middle pleistocene saalian lake outburst floods in the munsterland embayment nw germany impacts and magnitudes abstract during the late saalian drenthe glaciation ice damming of the upper weser valley led to the formation of glacial lake weser the lake drained catastrophically into the munsterland embayment as the western ice dam failed releasing up to 110 km3 of water with a calculated peak discharge of 2 5 105 m3 s to 1 3 106 m3 s geographic information systems gis and high resolution digital elevation models dem were used to map streamlined landforms and channel systems in front of lake overspills geological maps 2450 boreholes and the dem were integrated into the 3d modeling program gocad to reconstruct the distribution of flood related deposits palaeotopographic surfaces and the internal facies architecture of streamlined hills the drainage pathways are characterized by the occurrence of deep plunge pools channels streamlined hills and 4 km long and 12 m deep v shaped megaflutes plunge pools are deeply incised into mesozoic basement rocks and occur in front of three major overspill channels the plunge pools are up to 780 m long 400 m wide and 35 m deep approximately 1 10 5 km downslope of the overspill channels fan shaped arrays of streamlined hills are developed each covering an area of 60 130 km2 indicating rapid flow expansion the hills commonly have quadrilateral to elongated shapes and formed under submerged to partly submerged flow conditions when the outburst flood entered a shallow lake in the munsterland embayment hills are up to 4300 m long 1200 m wide 11 m high and have characteristic average aspect ratios of 1 3 3 they are separated by shallow anabranching channels in the outer zones and up to 30 m deep channels in the central zones hills partly display v shaped chevron like bedforms that have apices facing upslope are 1 6 2 5 km long 3 10 m high 0 8 1 2 m from limb to limb with limb separation angels of 20 35 these bedforms are interpreted as mixed erosional depositional features it is hypothesized that the post saalian landscape evolution of the munsterland embayment has considerably been influenced by catastrophic floods of glacial lake weser creating large and deep valleys which subsequently became the new site of river systems the outburst floods probably followed the east west trending saalian rhine meuse river system eventually flowing into the north sea the strait of dover and the bay of biscay it is speculated that the hondsrug ice stream may have been enhanced or even triggered by the formation and outburst of glacial lakes in the study area

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

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

sedimentology and paleohydrology of glacial lake outburst deposits in southeastern saskatchewan and northwestern north dakota glacial lake outbursts occurred in the northern great plains as ice marginal lakes suddenly drained forming an interconnected system of glacial lake spillways the outbursts were highly erosive and consequently deposits from such discharges are rare in the spillways glacial lake outburst deposits in the souris des lacs and moose mountain spillways saskatchewan and north dakota have distinct bar shapes and internally are more massive and homogeneous than those of outwash systems in this paper the outburst deposits are described and the sedimentologic and hydrodynamic characteristics of the outburst discharges are interpreted coarse grained sediment eroded from till formed large scale bars in the spillways as much as 2 km long and 30 m thick both as pendant bars and bars in alcoves next to contemporaneous landslides internally the bars consist of homogeneous masses of massive matrix supported very poorly sorted pebbly cobble gravel containing boulders as much as 3 m in diameter the maximum particle sizes in individual bars decrease downstream and toward spillway sides the lithology of the bars resembles the local glacial drift material from the tertiary bedrock in which the spillways are partially incised is not concentrated in the bars paleohydraulic calculations based on data of maximum particle size and on the shields9 entrainment function yield unreasonably large values supplementary calculations based on depth limits established from field observations yield realistic values this method indicates that velocities of 2 9 to 11 7 ms 1 and discharges of 5 8 10 4 to 8 2 10 5 m 3 s 1 were achieved by the outburst sediment water concentrations during the outburst estimated by dividing the volume of sediment eroded by the source lake volume averaged 20 by weight because of this estimate the abundant amount of fine grained material that was eroded and structure of the outburst deposits we infer that outburst flows were hyperconcentrated with sediment water concentrations being as much as 40 by weight in some areas we further infer that sediment transport was extremely efficient and that most particles including coarse gravel were transported in suspension this interpretation is consistent with the sedimentology of the deposits and other conjectural evidence expanding sections caused coarser sediment to be deposited indiscriminate of clast size as poorly sorted massive gravel bars finer grained sediment sand to clay size was transported through the spillway system into downstream glacial lakes

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

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

late devonian tetrapod habitats indicated by palaeosols in pennsylvania abstract late devonian famennian tetrapods from the duncannon member of the catskill formation near hyner pennsylvania usa have been found within palaeosols that offer a new line of evidence for their ancient environments hyner has yielded at least two fossil tetrapod species hynerpeton basseti and densignathus rowei subhumid vertisol palaeosols and semiarid aridisol palaeosols alternate at hyner as in other catskill formation sedimentary cycles attributed to milankovitch eccentricity periods 100 ka tetrapods were found in palaeosols of subhumid not semiarid phases of 100 ka palaeoclimate cycles in addition palaeosols at hyner record an unusually warm and wet climatic episode compared with other palaeosols of the catskill formation and correlated with the european annulata black shale event tetrapod bones are cracked and disarticulated in red palaeosols of an oxbow lake margin as if victims of dry season death decay and subaerial weathering vegetation choked swales and floodplains would have afforded shelter from 3 4 m long predatory fish hyneria lindae of open water and offered food of large dead fish small live fish arachnids myriapods and scorpions if these early tetrapods lived on land at all it was during wet seasons of feeding and breeding rather than fatally dry seasons supplementary material chemical data are available at http www geolsoc org uk sup18373

woodland hypothesis for devonian tetrapod evolution abstractthe rarity of devonian tetrapods and the absence of tetrapods during the first 14 million years of the mississippian romer s gap have inspired hypotheses of fish tetrapod evolutionary transition as an escape from difficult habitats such as deserts or stagnant waters these hypotheses and romer s gap are tested here using depth to calcic horizon in paleosols of the northern appalachians as a proxy for precipitation and vegetation changes during the devonian and mississippian all tetrapod bones and trackways in this region as well as fossil tree remains were found at times of high precipitation indicated by deep calcic paleosols when subhumid woodlands expanded at the expense of semiarid shrublands in alluvial lowlands no tetrapods or tree fossils were found in abundant paleosols with the shallow calcic horizons of aridland soils the mean annual precipitation requirement of devonian mississippian tetrapods and trees was at least mm global distribution of prototetrapods and aquatic tetrapo

three dimensional sequence analysis of a subsurface carbonate ramp mississippian appalachian foreland basin west virginia usa well cuttings wireline logs and limited core and outcrop data were used to generate a regional three dimensional sequence framework for upper mississippian chesterian greenbrier group carbonates in the appalachian foreland basin west virginia usa the resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio eustasy during the transition into ice house conditions the ramp facies include inner ramp red beds and aeolianites lagoonal muddy carbonates mid ramp ooid and skeletal grainstone shoal complexes and outer ramp wackestone mudstone that grades downslope into laminated silty lime mudstone the facies make up fourth order sequences a few metres to over 90 m 300 ft thick the sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones on the ramp sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites and only a few are calichified maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units on the shallow ramp maximum flooding surfaces overlie siliciclastic prone transgressive systems tracts that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones the fourth order sequences are the major mappable subsurface units they are bundled into weak composite sequences which are bounded by red beds in spite of differential subsidence rates across the foreland basin 1 to 3 cm k y up to 25 cm k y eustatic sea level changes controlled regional sequence development thrust load induced differential subsidence of fault blocks coupled with in plane stress controlled the rapid basinward thickening of the depositional wedge whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin

evidence for long term climate change in upper devonian strata of the central appalachians abstract the highest 1 to 200 m of the upper devonian famennian catskill and equivalent hampshire formations exhibit a noticeable vertical or stratigraphic change in color and a shift in lithologic character the lower part of the unit is characterized by typically red channel phase sandstones and overbank siltstone and mudstone containing thin calcareous paleosols these lithologies give way to greenish gray sandstone containing abundant coaly plant fragments coalified logs and pyrite interbedded with thick intervals of non calcareous paleo vertisols the increase in the prominence of preserved terrestrial organic matter suggests that there was a corresponding increase in the abundance of plants in terrestrial ecosystems the stratigraphic change in lithology within the upper part of the catskill hampshire succession suggests the onset of environmental conditions that became increasingly wet in response to elevated humid climatic conditions during the final stages of catskill alluvial plain deposition the sedimentological signature suggesting increased climatic wetness within the uppermost catskill and hampshire formations is nearly contemporaneous with the initiation of late devonian gondwanan glaciation in the paleo high latitudes the appalachian climate record indicates that this change began during the fa2c and continued through the latest famennian reaching its peak during the fa2d when glacial deposits are recorded in the paleo mid latitudes of the appalachian basin evidence of this late famennian increase in precipitation also is recorded in the adjacent marine environments equivalent age marine units in ohio and kentucky record progressive increases in both total organic carbon and the percentage of terrestrially derived organic carbon this suggests that there was a late famennian increase in terrestrial organic matter productivity and that during the late famennian there were elevated levels of runoff produced by the interpreted increase in precipitation that washed progressively higher amounts of terrestrial organic matter into the local marine environments the late famennian climate changes identified within the appalachian basin strata have been recognizable globally and appear to have had both positive and negative effects on the earth s biota some marine groups exhibit sharp diversity drops or even extinction coincident with the maximum development of the late famennian ice age conversely terrestrial biota appears to have been more positively affected by the late famennian increased wetness that accompanied this progressive climate change marked diversification and evolutionary innovation which appear to coincide with this climatic deviation can be recognized within terrestrial plant communities and early tetrapod amphibians

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

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

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

genetic stratigraphy and depositional systems of the upper devonian lower mississippian price rockwell deltaic complex in the central appalachians u s a abstract rocks of the price and rockwell formations comprise the uppermost devonian lower mississippian deltaic complex in the central appalachians the price formation is dominantly marine and refers to all uppermost devonian lower mississippian rocks above either hampshire group red beds or the marine greenland gap formation and below either the greenbrier limestone group or maccrady formation red beds in the central appalachians the rockwell formation is dominantly non marine and refers to equivalent rocks in south central pennsylvania and the maryland west virginia panhandle region members of the price formation are generally equivalent to discrete genetic events price deposition was initiated in latest devonian time when a regional transgression covered delta and alluvial plain facies of the catskill deltaic complex with protected bay and strandline facies of the oswayo member in west virginia pennsylvania and western maryland farther south these transgressive facies overlie the cloyd conglomerate member a thin regressive transgressive sedimentary wedge and occur in the lower part of the sunbury shale member subsurface berea sandstone deposition corresponded to regional exposure and erosion in the outcrop belt this unconformable surface was overstepped in earliest mississippian time by a major transgression that deposited a variably thick but persistent basal transgressive sandstone during shoreface retreat sandstones that have been referred to the cussewago sandstone in northern west virginia and southwest pennsylvania are part of this basal sandstone eastward these sandstones thicken coarsen and interbed with a polymictic diamictite at the base of the rockwell formation shaly facies of the earliest mississippian transgression overlie the basal sandstone the riddlesburg shale preserves offshore and open bay facies in west virginia that grade eastward to estuarine and restricted back bar lagoon and marsh facies of a barred bay complex in south central pennsylvania and the maryland west virginia panhandle from central west virginia riddlesburg facies grade southward into basinal facies of the sunbury shale member syndepositionally active basement features the west virginia dome and tri state block were structurally positive areas in the foreland basin the tri state block caused truncation of lower mississippian marine facies in western maryland and large scale westward erosional overlap of channel fill sandstones in the upper rockwell formation the west virginia dome was also structurally positive and the basal transgressive sandstone contains phosphatic omission surfaces on the dome crest lack of subsidence caused scour and incision of riddlesburg facies by overlying deltaic facies progradation ensued with fluvial dominant shallow water deltaic systems price rockwell member in northern west virginia and marine dominant deep water deltaic facies farther south a 150 m minimum paleodepth estimate in the foreland basin is based on stratigraphic thickness in southern west virginia following a transgression near the kinderhookian osagean boundary price marine deltaic facies form a coarsening upward sequence to delta plain coals and coastal alluvial plain red beds a 35 m estimate for average storm wave base utilized tempestite proximal distal trends

water sheet outburst floods from the laurentide ice sheet field evidence and a theoretical model support the concept that during wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the hudson bay ba

catastrophic flood hypothesis for the origin of the souris spillway saskatchewan and north dakota glacial lake spillways in the midcontinent region consist of narrow deep trenches connecting proglacial lake basins geomorphic and sedimentologic evidence from the souris and des lacs spillways in saskatchewan and north dakota indicates a catastrophic drainage of glacial lake regina the souris spillway in saskatchewan is composed of a broad upper scoured surface 5 to 10 km wide which merges with the floor of glacial lake regina the upper surface is longitudinally grooved and mantled with coarse lag deposits an inner trench 1 km wide and 20 to 45 m deep occupies the center of the spillway the two level morphology of the spillway probably developed by initial erosion of the upper level followed by incision of the inner trench a sequence of events shown by flume experiments performed by shepherd and schumm near the saskatchewan and north dakota border the flood water bifurcated into two branches as part of the water spilled over a divide into another spillway channel the two spillways in north dakota pre existing meltwater channels were occupied and enlarged by the discharge from glacial lake regina along the path of the spillways leading to the glacial lake souris basin water repeatedly breached the sides of the channels eroding shallow channels leading away from the spillway near minot north dakota a significant amount of the water spilled out toward the east and eroded a plexus of anastomosing channels with streamlined erosional remnants between the channels deposits of the flood include huge point bars located at the inside of each channel meander internally the bars generally consist of poorly sorted indistinctly bedded coarse gravel containing boulders of resistant and nonresistant lithologies as much as 3 m in diameter peak discharge of 1 10 5 m 3 s or more may have been achieved at the outlet of the lake at this rate glacial lake regina would have drained rapidly probably in less than a month the most likely cause for the rapid drainage of such proglacial lakes as glacial lake regina was high discharge inflow of water from an upstream source along the ice margin

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

carbon oxygen isotope signal of mississippian slope carbonates appalachians usa a complex response to climate driven fourth order glacio eustasy abstract mississippian chesterian ramp slope muds in virginia deposited on the margin of a rapidly subsiding foreland basin were not significantly reset isotopically by regional meteoric aquifer systems that affected units on the adjacent platform carbon and oxygen isotopic ratios of these muds tend to covary at the scale of the twelve 4th order sequences that dominate the platform succession the 13 c values of the slope muds range from 0 5 to 4 pdb and lie in the range of least altered contemporaneous brachiopods from north america indicating little resetting of carbon isotopes by diagenesis there is an approximately 1 to 2 decrease in 13 c in the maximum flooding zone relative to the lowstand followed by a positive shift upward in the highstand before becoming more negative toward 4th order correlative conformities meteoric diagenesis might have reset some sediments just beneath a sequence boundary to lighter values it cannot account for the observed shifts evident throughout the sequences the 13 c enriched values in 13 c profiles could be due to increased productivity during glacial stages the increased productivity during glacial stages was probably due to increased ocean circulation coupled with shallowing which brought the ramp top into waters with more 13 c enriched dissolved inorganic carbon with the opposite effects occurring during deglaciation the 18 o values of muds range from about 2 2 to about 4 6 pdb falling within and beyond the lighter part of the range of contemporaneous north american brachiopods mii h s grossman e l yancey t e 1999 carboniferous isotope stratigraphies of north america implications for carboniferous paleoceanography and mississippian glaciation geol soc am bull 111 960 973 these values likely have been reset by burial diagenesis and perhaps by some meteoric diagenesis just beneath correlative conformities the sequences show negative excursions of 1 to 2 in 18 o in the maximum flooding zone relative to the lowstand and then become more positive upward in the highstand then decrease toward the correlative conformities some of the preserved signal could reflect ice volume changes although this would account for only 0 5 to 1 change the ice volume effect during lowstands plus cooling of ramp top waters and small increases in salinity due to increased aridity in the appalachian basin could account for the remaining 0 5 to 1 5 of oxygen isotope excursions with the opposite effect occurring during high sea levels the 18 o and 13 c of the appalachian ramp slope facies lack the strong 3rd order trends of the mid continental united states and europe the remnant 4th order carbon and oxygen isotope signal is similar in structure to cenozoic deep sea isotope profiles that are due in large part to 4th order glacio eustasy this would be compatible with onset of late paleozoic glaciation of gondwana

sequence stratigraphic analysis using well cuttings mississippian greenbrier group west virginia well cuttings analysis predates modern carbonate facies analysis sequence stratigraphy seismic reflection surveys and advanced geophysical logging techniques these newer methods have resulted in well cuttings becoming less important as a major source of data for high resolution subsurface analysis binocular analysis of well indurated paleozoic well cuttings can be used to construct detailed vertical facies successions in wells when tied to wire line logs facies analysis can then be used to construct higher resolution sequence stratigraphic frameworks and time slice maps this approach was tested on mississippian carbonates in the appalachian basin of west virginia the analysis was done using the washed coarse fraction 1 2 mm 0 04 0 08 in of the cuttings for each sample interval classified according to dunham rock type counted to determine relative abundance and plotted as percent lithology versus depth for each well digitized wire line logs and the cuttings percent logs were adjusted typically 10 ft 3 m or so to consider drilling lag lithologic columns were produced from the combined data and sequences were picked gamma ray markers were used to correlate the sections and sequence stratigraphic cross sections were produced time slice maps were generated that show the thickness of the individual sequences and the distribution of major facies within systems tracts this approach generated a rock based high resolution sequence framework for the reservoir and led to a much better understanding of controls on the distribution and stacking of reservoirs

the role of sediment supply in esker formation and ice tunnel evolution abstract meltwater is an important part of the glacier system as it can directly influence ice sheet dynamics although it is important that ice sheet models incorporate accurate information about subglacial meltwater processes the relative inaccessibility of contemporary ice sheet beds makes direct investigation challenging former ice sheet beds contain a wealth of meltwater landforms such as eskers that if accurately interpreted can provide detailed insight into the hydrology of former ice sheets eskers are the casts of ice walled channels and are a common landform within the footprint of the last laurentide and cordilleran ice sheets in south western alberta esker distribution suggests that both water and sediment supply may have been important controls the longest esker ridge segments are located within meltwater valleys partially filled by glaciofluvial sediments whereas the shortest esker ridge segments are located in areas dominated by clast poor till through detailed esker ridge planform and crest type mapping and near surface geophysics we reveal morpho sedimentary relationships that suggest esker sedimentation was dynamic but that esker distribution and architecture were primarily governed by sediment supply through comparison of these data with data from eskers elsewhere we suggest three formative scenarios 1 where sediment supply and flow powers were high coarse sediment loads result in rapid deposition and rates of thermo mechanical ice tunnel growth is exceeded by the rate of ice tunnel closure due to sediment infilling high sedimentation rates reduce ice tunnel cross sectional area cause an increase in meltwater flow velocity and force ice tunnel growth thus ice tunnel growth is fastest where sedimentation rate is highest this positive feedback results in a non uniform ice tunnel geometry and favours macroform development and non uniform ridge geometry 2 where sediment supply is limited but flow power high the rate of sedimentation is less than the rate of thermo mechanical ice tunnel growth here the ice tunnel enlarges faster than it fills with sediment and its evolution is independent of sedimentation resulting in more uniform ice tunnel geometry in these cases esker architecture is dominated by extensive vertical accretion of tabular units and ridge geometry is more uniform 3 where sediment is truly supply limited the sedimentation rate is negligible regardless of water supply and like scenario 2 ice tunnel growth is independent of sediment deposition forming a relatively uniform ice tunnel or eroding the bed because meltwater flows transport few gravel clasts the ice tunnel is not completely filled with gravel and instead saturated and pressurized diamicton or bedrock if deformable from beneath the surrounding ice is squeezed into the relatively low pressure ice tunnel during waning flow or after ice tunnel shutdown resulting in deformation of limited gravels deposited within the ice tunnel and a landform cored with diamicton or deformed bedrock and with a relatively uniform ridge geometry our data demonstrate that an esker map is a minimum map of ice walled channel location and that continued detailed investigation of morpho sedimentary relationships is essential to gaining a complete picture of esker forming processes validating the morpho sedimentary relationships identified in south western alberta and other areas with a larger data set may allow improved remote predictive esker mapping over larger areas and inferences to be made about spatial and temporal variations in esker depositional environments and ice tunnel evolution

streamlined erosional residuals and drumlins in central british columbia canada abstract the upland lowland pattern in the plateau region of central british columbia canada forms an extremely large anastomosing channel network with the uplands representing interfluves between channels the study area landscape is remarkably similar in form to water produced channel systems and qualitatively resembles flood landscapes from the channelled scablands and the margins of the laurentide ice sheet numerical shape analysis of the area erosional residuals gives similar results as those derived from known flood landscapes the length to width ratios of the uplands l w 2 38 r2 0 89 are similar to those reported for braid bars and erosional residuals formed by glacial outburst floods thus the study area landscape records a megaflood or floods that almost completely immersed the landscape drumlins with in places ubiquitous hairpin furrows locations downstream from steep slopes facing into the flow and eroded into till and bedrock similarly reflect regional scale meltwater flow that immersed the landscape the regional flow submerged the anastomosing channels at the time of drumlin formation drumlins likely formed as the anastomosing network developed divergent drumlin orientations probably reflect either late flow or separate drumlin forming events that did not appreciably alter the anastomosing system

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

shapes of streamlined islands on earth and mars experiments and analyses of the minimum drag form streamlined islands in rivers and comparable landforms in the channeled scabland of washington and in the outflow channels on mars have shapes that are closely similar to symmetrical airfoils with length width ratios averaging 3 to 4 a review of measurements of drag on airfoils demonstrates that a minimum total drag is achieved at such length width ratios supporting the hypothesis that these islands acquired shapes that minimized the drag or resistance to the flowing fluid when they were formed this minimum drag is achieved by the reduction of the wake while maintaining a small skin friction flume experiments were undertaken with model islands to examine how they achieve their streamlined form when the island is not fully submerged a combined bow wave and hydraulic drop play a major role in their erosion but most of the streamlining is brought about by deposition filling the wake region when the island is submerged the flow over the top can become supercritical producing a hydraulic jump in the island lee and focusing the erosion in that region rapidly eroding the island to a streamlined shape these experiments are consistent with the prototype streamlined islands duplicating many of their features

drumlin formation by subglacial meltwater erosion some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater the lengths of these ridges vary in scale from a few tens of millimetres to over 5 km similar form elements are illustrated for three scales of forms it is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials this erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities the unifying factor for both theories is the role of sheets of subglacial meltwater

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

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis