subglacial deforming bed conditions recorded by late quaternary sediments exposed in vineland quarry ontario canada abstract there has been considerable interest in recent years in the development of theoretical models of subglacial transport and deposition of sediment but relatively few studies report field documentation of the resultant sediment stratigraphies this paper presents detailed sedimentological description and analysis of a succession of late quaternary deposits interpreted to record subglacial overriding and deformation of previously deposited lacustrine sediments exposed in the vineland quarry that sits close to the crest of the niagara escarpment within the lake ontario basin the predominately fine grained sediments record deposition under glaciolacustrine conditions followed by deformation and deposition by overriding glacial ice laminated silt and clay deposits overlie the striated bedrock surface and were deposited within a lake that formed as the ontario lobe of the laurentide ice sheet advanced during the port huron stadial and ponded water against the niagara escarpment the laminated silt and clay facies show increasing amounts of deformation up section passing from planar through ductile to brittle deformation this succession of deformed facies is overlain by a macroscopically massive clay rich diamict that caps the section this pattern of sediment deposition and deformation is consistent with that proposed by current models of subglacial sediment deformation with the disrupted laminated silts and clays representing glacitectonites resulting from downward penetrating stresses imparted by an overriding ice sheet the uppermost massive diamict unit represents full macroscopic homogenization of the overridden sediment and is classified as a subglacial traction till the gradual transition from undisturbed laminated deposits through increasingly deformed sediment to structureless diamict suggests that these deposits record a single episode of ice advance across the region this ice advance was probably the short lived advance of the ontario lobe of the laurentide ice sheet that occurred at approximately 13 000 ybp

stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

sedimentological history of bryant canyon area northwest gulf of mexico during the last 135 kyr marine isotope stages 1 6 a proxy record of mississippi river discharge abstract bryant and eastern canyons are located in northwest gulf of mexico and are characterized by a complex sedimentological history related to glacioeustatic cycles river discharges and interactions between depositional and halokinetic processes this study is based on detailed sedimentological analysis from forty eight long cores from these two canyons this paper determines the evolutionary history of the canyons and assesses the response of sedimentary processes to morphological climatic hydrological and sea level changes during the last glaciation the upper and middle continental slope was supplied with sediments by low density turbidity currents derived from the depositional segregation deposition of the coarsest material in the most proximal locations of large turbidity currents initiated on the outer shelf the lower continental slope was supplied with sediment by westward flowing bottom currents originated from the entrainment of the most diluted wash load and tails of turbidity currents from the mississippi fan bryant and eastern canyon systems were active during the penultimate glaciation marine isotope stage mis 6 and were supplied with sediments by an ancestral shelf margin mississippi river delta gravity flows transported enormous amounts of sediment to the continental slope and abyssal plain of the northwest gulf of mexico the sea level rise at mis 5 led to confinement of river sourced sediments to the widespread continental shelf of the northwest gulf of mexico and consequently to the cessation of gravity flows during the first 40 kyr of mis 5 salt diapirs transformed the canyons into a network of intraslope basins the sea level dropped to the mid shelf during mis 3 and 4 but never reached the shelf break and therefore river sourced sediments remained largely confined to the shelf however seaward sediment transportation was achieved occasionally through turbidity currents related to sediment failures storms and high river discharges four high river discharge events have been identified during this period the first three were centred at 37 45 and 53 cal ka bp the last high river discharge occurred at the end of mis 3 29 4 33 2 cal ka bp and resulted in the deposition of closely spaced mud turbidites over the entire continental slope the laurentide ice sheet lis was restricted north of the upper mississippi river valley during 60 to 30 cal ka bp and therefore the high river discharge events are interpreted as melt water events related to brief southward advancements of the lis which resulted in the flooding of mississippi river the extensive lowering of sea level during the last glacial maximum mis 2 resulted in the almost direct discharge of mississippi river sediments to the upper continental slope leading to the development of abundant turbidity currents eleven wet dry cycles during this period are defined they probably originated from episodic subglacial melt water floods released from southern parts of the lis the last deglaciation event is characterized by the development of a major melt water event at 16 5 13 cal ka bp that resulted in the deposition of distinct organic rich sediments at about 13 cal ka bp the melt water discharges of the lis in north america switched from the mississippi river to either the st lawrence or mackenzie river valleys causing the domination of hemipelagic sedimentation on the continental slope of the northwest gulf of mexico isotopic data indicate that melt water discharges returned to the mississippi river valley at 11 4 cal ka bp the absence of any sedimentological indication on the continental slope of the northwest gulf of mexico of the return of the melt water discharges to the mississippi river is attributed to the confinement of river sourced sediments on the continental shelf due to the rise of the sea level

three dimensional architecture and hydrostratigraphy of cross cutting buried valleys using airborne electromagnetics glaciated central lowlands nebraska usa buried valleys are characteristic features of glaciated landscapes and their deposits host important aquifers worldwide understanding the stratigraphic architecture of these deposits is essential for protecting groundwater and interpreting sedimentary processes in subglacial and ice marginal environments the relationships between depositional architecture topography and hydrostratigraphy in dissected pre illinoian till sheets is poorly understood boreholes alone are inadequate to characterize the complex geology of buried valleys but airborne electromagnetic surveys have proven useful for this purpose a key question is whether the sedimentary architecture of buried valleys can be interpreted from airborne electromagnetic profiles this study employs airborne electromagnetic resistivity profiles to interpret the three dimensional sedimentary architecture of cross cutting buried valleys in a ca 400 km2 area along the western margin of laurentide glaciation in north america a progenitor bedrock valley is succeeded by at least five generations of tunnel valleys that become progressively younger northward tunnel valley infills are highly variable reflecting under filled and over filled conditions under filled tunnel valleys are expressed on the modern landscape and contain fine sediments that act as hydraulic barriers over filled tunnel valleys are not recognized in the modern landscape but where they are present they form hydraulic windows between deep aquifer units and the land surface the interpretation of tunnel valley genesis herein provides evidence of the relationships between depositional processes and glacial landforms in a dissected pre illinoian till sheet and contributes to the understanding of the complex physical hydrology of glacial aquifers in general this article is protected by copyright all rights reserved

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

geological model and development of the cenozoic wiang pa pao basin chiang rai province northern thailand based on gravity data modelling and surface structural interpretation abstract 3 d inverse gravity modelling constrained by surface geological data across the neogene wiang pa pao basin wpb northern thailand provides new subsurface models of the basin geometry and its structural development the intermontaine wpb is seismically active and exhibits many geothermal sites both are indicative of active fault zones six hundred thirty six terrestrial gravity stations with 500 m spacing were acquired the residual complete bouguer anomaly map cba reveals an n s elongate basin characterized by gravity lows bounded by gravity highs on the eastern margin of the basin metasedimentary basement and moderate gravity anomalies on the western margin granitic basement structural edge detection revealed n s trending faults along the eastern and western margins linked by ne sw and nw se trending lineaments the 3 d gravity model indicates an asymmetric graben with a maximum depocenter depth of 1300 m surface structure and seismicity confirm the gravity interpretation that the wpb is a dextral transtensional basin characterized by wsw ene trending r shears and nne ssw r shears distributed in duplex like geometries along the n s trending principal displacement zone the wpb displays unusually well developed r shears where palaeozoic metasedimentary rocks in the basement and cenozoic basin sediments are present these faults disappear to the south where the main n s fault resides entirely within the granite the wpb is associated with cenozoic multi phase rifting in the late oligocene miocene major rift basins formed under w e extension strongly influenced by wsw ene to ne sw and nw se pre existing trends in the latest miocene recent the younger basins including the wpb underwent dextral strike slip along new and existing n s dextral fault trends

bedform signature of a west antarctic palaeo ice stream reveals a multi temporal record of flow and substrate control abstract the presence of a complex bedform arrangement on the sea floor of the continental shelf in the western amundsen sea embayment west antarctica indicates a multi temporal record of flow related to the activity of one or more ice streams in the past mapping and division of the bedforms into distinct landform assemblages reveals their time transgressive history which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo ice velocity as suggested previously a main control on the bedform imprint is the geology of the shelf which is divided broadly between rough bedrock on the inner shelf and smooth dipping sedimentary strata on the middle to outer shelf inner shelf bedform variability is well preserved revealing information about local complex basal ice conditions meltwater flow and ice dynamics over time these details which are not apparent at the scale of regional morphological studies indicate that past ice streams flowed across the entire shelf at times and often had onset zones that lay within the interior of the antarctic ice sheet today in contrast highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow and may be a truer representation of fast palaeo ice flow in these locations a revised model for ice streams on the shelf captures complicated multi temporal bedform patterns associated with an antarctic palaeo ice stream for the first time and confirms a strong substrate control on a major ice stream system that drained the west antarctic ice sheet during the late quaternary

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

sedimentologic evidence for outburst floods from the laurentide ice sheet margin in wisconsin usa implications for tunnel channel formation abstract clast supported boulder gravel in outwash fans along the glacial maximum margin of the laurentide ice sheet in wisconsin indicates the occurrence of outburst floods these sediments with clast intermediate axes of up to 2 m are located downstream of tunnel channels and were deposited shortly before cessation of glaciofluvial activity on each fan since tunnel channels with fans are widespread along the ice sheet margin in the western great lakes region these outburst floods were probably common paleodischarge estimates derived from the boulder deposits are poorly constrained but values of at least several hundred m3 s 1 are likely four potential water sources for the floods exist an extreme surface melt event an extreme precipitation event drainage of supraglacial lakes or drainage of stored subglacial meltwater we focus on the storage of subglacial meltwater behind the ice sheet margin as proglacial permafrost was present as ice advanced to its maximum extent and a frozen bed zone upstream from the margin probably impeded drainage through groundwater aquifers decay of this permafrost seal would have eventually allowed trapped water to drain through the tunnel channels we suggest that the 2 m boulders were entrained in an outburst of subglacial water that enlarged a pre existing channel cut by ablation derived flows

light hydrocarbons and diamondoids of light oils in deep reservoirs of shuntuoguole low uplift tarim basin implication for the evaluation on thermal maturity secondary alteration and source characteristics abstract the shuntuoguole low uplift in tarim basin is particular because it provides insights into geochemistry of light oils at ultra deep ordovician oil reservoirs 7200 8200 m the light hydrocarbons and diamondoids of 16 oil samples from shunbei no i fault zone f1 and v fault zone f5 were analyzed to investigate their thermal maturity source characteristics and secondary alteration the oils show high similarity in the characteristics of light hydrocarbons and diamondoids the light hydrocarbons are characterized by high contents of alkanes and low contents of cycloalkanes and aromatics and the diamondoids show a domination of adamantanes and their alkylated isomers compared diamantanes thermal maturity indicators derived from diamondoids and c5 c7 light hydrocarbons indicate that the oils are highly mature and the corresponding equivalent vitrinite reflectance rc determined by light hydrocarbons and methyldiadamantane index are in the ranges of 1 2 1 5 signatures of biodegradation and thermochemical sulfate reduction were not observed in the oils the geochemical information from the light hydrocarbons and distribution patterns of molar concentration of n alkanes indicate that the oils from f1 experienced noticeable evaporative fractionation and the oils from f5 did not this was supposed to be the primarily reason for the physical difference between oils from the both fault zones the parameters derived from the light hydrocarbons and diamondoids indicate the oils are from same source rocks which are associated with marine materials with type ii kerogen such as algae and bacteria and both of cambrian lower ordovician o1 and middle upper ordovician o2 3 source rocks in the deep lower palaeozoic strata contributed to the oils

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

morphology and origin of the fair oaks dunes in nw indiana usa abstract the fair oaks dunes fod of nw indiana usa is a large 4500 km 2 inland dune field associated with the late wisconsin deglaciation of the laurentide ice sheet meltwaters released by the michigan saginaw and huron erie lobes transported fluvioglacial sediment through the kankakee and tippecanoe valleys and their tributaries the texture and composition of the sand in the fod suggest a saginaw lobe origin of sediment with some huron erie lobe sediment sub mature sand with sub angular grains and a large feldspar content suggests relatively short distance of transport during two or possibly three dune building and dune reworking events we propose a model which explains the development of the dunes in three stages dune development began during the bolling allerod stage 1 15 13 ka interval during this stage anticyclonic easterly and north easterly winds deflated the sand from outwash deposits and built transverse and barchanoid dunes on the western sides of the tippecanoe valley and paleo channels further downwind on the western and southwestern windward margins of the fod loess was deposited during the early younger dryas stage 2 12 5 ka atmospheric circulation changed and westerly winds reworked the original dunes to create a great variety of parabolic dunes simple hemicyclic and lobate parabolic dunes developed in the western fod while further downwind in the eastern and the southern fod more elongated hairpin and windrift dunes developed on the upwind side of the dune field loess deposits remained stable and were not remobilized during the second stage dune development by the early holocene the fod dunes were stabilized until their minor remobilization during the middle holocene stage 3 minor disturbances caused by anthropogenic activities have occurred in last two centuries

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

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

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

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

late wisconsinan drift stratigraphy of the lake michigan lobe in southwestern michigan three lake michigan lobe till sheets are exposed in a 20 to 25 m high section glenn shores section along the lake michigan shoreline in southwestern michigan the glenn shores till lowest is directly overlain by stratified silt sand and gravel containing organic material dated at 37 150 to 48 000 yr b p the ganges till middle and saugatuck till uppermost are overlain by lacustrine sediments the three till units can be differentiated by the 7a 10a x ray diffraction peak height ratio of their clay size fraction clay mineral analyses of more than 200 samples collected from moraines till plains and multi till exposures 2 to 60 km inland suggest that saugatuck till at the lakeshore is equivalent to till in the lake border valparaiso and sturgis kalamazoo morainic systems whereas ganges till can be traced in the subsurface from the lakeshore to where it crops out within the tekonsha moraine the presence of lacustrine sediments between ganges and saugatuck tills implies that a significant retreat 60 km of the lake michigan lobe occurred between the formation of the tekonsha moraine and that of the sturgis kalamazoo morainic system on the basis of morainal correlations we propose that saugatuck till correlates with wadsworth till in illinois whereas ganges till probably correlates with the upper part of the yorkville till in illinois

wrench related folding a case study of bohai sea basin china abstract wrench motion is relatively common in basins but often goes undetected because of its subtle structural imprint even so wrench related folding is of significance in petroleum exploration and development based on the riedel shear nomenclature we apply the model of wrench related folding to deformation in the bohai sea basin the folding related to r shears t tensional structural systems t systems and c compressive structural systems c systems in a riedel shear model are discussed the r system related folding results from differential movements between the two sides of fault blocks in map view the fold is oriented 90 2 in the initial deformation stage or more than 90 2 from the principle displacement zone pdz where is the angle of internal friction the t system related folding is related to the rollover of the hanging wall and in map view the fold is initiated at 45 from the pdz in the initial deformation stage the c system related folding is resulted from the compression induced by a wrench action in map view the fold was oriented 45 from initial deformation in the pdz bohai sea basin fold orientations fit our models and the wrench related folds play important roles in oil and gas accumulation

formation of subglacial till under transient bed conditions deposition deformation and basal decoupling under a weichselian ice sheet lobe central poland a multi proxy approach involving a study of sediment architecture grain size grain roundness and crushing index petrographic and clay mineral composition till fabric and till micromorphology was applied to infer processes of till formation and deformation under a weichselian ice sheet at kurzetnik poland the succession consists of three superposed till units overlying outwash sediments deformed at the top the textural characteristics of tills vary little throughout the till thickness whereas structural appearance is diversified including massive and bedded regions indicators of intergranular bed deformation include overturned attenuated folds boudinage structures a sediment mixing zone grain crushing microstructural lineations grain stacking and high fabric strength lodgement proxies are grooved intra till surfaces ploughing marks and consistently striated clast surfaces basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers sand filled meltwater scours under pebbles and partly armoured till pellets it is suggested that the till experienced multiple transitions between lodgement deformation and basal decoupling cumulative strain was high but the depth of time transgressive deformation much lower centimetre range than the entire till thickness ca 2 m at any point in time consistent with the deforming bed mosaic model throughout most of ice overriding porewater pressure was high in the vicinity of glacier floatation pressure indicating that the substratum consisting of 11 m thick sand was unable to drain subglacial meltwater sufficiently

p t t constraints on the development of the doi inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt northern thailand abstract the western gneiss belt in northern thailand is exposed within two overlapping cenozoic structural domains the extensional doi inthanon metamorphic core complex domain located west of the chiang mai basin and the mae ping strike slip fault domain located west of the tak batholith new p t estimates and u pb and 40ar 39ar age determinations from the doi inthanon domain show that the gneiss there records a complex multi stage history that can be represented by a clockwise p t t path u pb zircon and titanite dating of mylonitic calc silicate gneiss from the mae wang area of the complex indicates that the paragneissic sequence experienced high grade medium pressure metamorphism m1 in the late triassic early jurassic ca 210 ma in good agreement with previously determined zircon ages from the underlying core orthogneiss exposed on doi inthanon late cretaceous monazite ages of 84 and 72 ma reported previously from the core orthogneiss are attributed to a thermal overprint m2 to upper amphibolite facies in the sillimanite field u pb zircon and monazite dating of granitic mylonite from the doi suthep area of the complex provides an upper age limit of 40 ma late eocene for the early stage s of development of the actual core complex by initially ductile low angle extensional shearing under lower amphibolite facies conditions m3 accompanied by near isothermal diapiric rise and decompression melting 40ar 39ar laserprobe dating of muscovite from both doi suthep and doi inthanon provided miocene ages of ca 26 15 ma representing cooling through the ca 350 c isotherm and marking late stage development of the core complex by detachment faulting of the cover rocks and isostatic uplift of the sheared core zone and mantling gneisses in the footwall similarities in the thermochronology of high grade gneisses exposed in the core complex and shear zone domains in the western gneiss belt of northern thailand and also in northern vietnam laos yunnan and central myanmar suggest a complex regional response to indentation of southeast asia by india

characterization of pebble fabrics in modern terrestrial glacigenic sediments pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers where sedimentary processes can be observed or inferred with relatively little ambiguity over 100 samples from contemporary environments illustrate fabrics characterizing melt out till deformed and undeformed lodgement till sediment flow deposits and ice slope colluvium lodgement till fabric variability is related to the two layer structure of these sediments a structureless friable upper layer with low shear strength and high consolidation coefficient overlying a very compact material of horizontal platy structure fabric strength assessed by eigenvalue analysis is weaker and pebble dip is more dispersed in the upper structureless horizon stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon alternatively upper horizon fabrics may be characteristic of all recently deposited lodgement tills with stronger fabrics developing at depth by dewatering and consolidation there is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt out tills through undeformed and deformed lodgement tills to sediment flow deposits and ice slope colluvium there is however considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some quaternary glacial sediments relatively strong fabrics characteristic of melt out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments

an ice contact rhythmite turbidite succession deposited during the november 1996 catastrophic outburst flood jokulhlaup skeiðararjokull iceland abstract this paper presents new evidence of coarse grained deposition from a turbulent suspension within a low energy slack water location during a recent well documented volcanically related high magnitude glacier outburst flood or jokulhlaup skei ararjokull iceland this study uses established spatial and temporal constraints on processes observed during the november 1996 jokulhlaup to interpret resultant flood sediments coarse grained sediments were deposited within flood slack water conditions from suspension load by repeated turbulent flow pulses with durations of seconds minutes depositional processes are thought to be analogous to turbidity currents a minimum thickness of 15 m of rhythmites record suspended sediment dynamics at a conduit mouth during the late rising and early falling stages of the jokulhlaup the morphology and sedimentology of deposits in a large ice walled chamber are consistent with previous models proposed for bar deposition during cataclysmic floods flood flows within subglacial conduits and ice walled open channels were sufficiently powerful to carry material up to boulder size in suspension macro turbulent flows carried huge quantities of suspended sediment to high levels within the main outlet channel high frequency short duration flow pulses entering a complex ice walled channel geometry generated highly unsteady and non uniform flows capable of both erosional and depositional work this study lends support to the deposition of multiple rhythmites per flood under main flow slack water conditions identification of high magnitude jokulhlaups in the ice marginal sedimentary record will depend on the identification and correct interpretation of feeder channel and slack water turbidite sediments the results described here may also have application to rhythmic deposits formed by large turbulent flows in other environmental settings

minimum limiting deglacial ages for the out of phase saginaw lobe of the laurentide ice sheet using optically stimulated luminescence osl and radiocarbon methods

the dimensions and topographic setting of antarctic subglacial lakes and implications for large scale water storage beneath continental ice sheets radio echo sounding res at 60 mhz has penetrated to the ice sheet bed on about 400 000 km of flight track covering more than 50 of the 13 5 x 106 km2 antarctic ice sheet about 70 subglacial lakes have been identified by characteristic strong mirror like and very flat res reflectors most are located in the ice sheet interior where numerical modeling predicts basal melting and 33 are within 100 km of the ice crest mean ice thickness above the lakes is about 3000 m about 75 of lakes have radio echo lengths of 30 km the largest is vostok lake which is 230 km long 14 000 km2 in area and has a water volume of about 2000 km3 more than 60 of lakes have maximum local bedrock elevations of 400 m and bed gradients of 0 1 adjacent to their margins extrapolating the observed side slope topography implies water depths from tens to several hundred meters in a few cases about 20 000 km2 of subglacial lakes are inferred from res which can be doubled for the entire ice sheet to yield an estimated total area of about 40 000 km2 excluding vostok lake assuming average lake depths between 50 and 250 m and including the 2000 km3 of water stored within vostok lake we calculate an envelope of about 4000 to 12 000 km3 for the likely volume of water stored in modern antarctic subglacial lakes equivalent to 10 35 mm of global sea level rise in these volume calculations it is assumed that no subglacial lakes the size of lake vostok remain to be discovered and that res length measurements along single transects are representative of overall lake dimensions our estimates of the total water volume of antarctic subglacial lakes which may be a suitable analogue for full glacial quaternary ice sheets do not necessarily conflict with the possible significance of large meltwater floods during the deglaciation of former midlatitude ice sheets

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

outburst flood origin of the central kalamazoo river valley michigan usa abstract geomorphic evidence and stratigraphic information from boreholes suggest that the oversized central kalamazoo river valley ckrv in southwest michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the saginaw lobe of the laurentide ice sheet the ckrv occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the lake michigan saginaw and huron erie lobes the course of the ckrv follows an irregular flow path that bisects the kalamazoo moraine of the lake michigan lobe erosional terraces near the mouth of the channel indicate that lake michigan lobe meltwater drained eastward prior to the westward saginaw outburst prior to valley formation the lake michigan lobe had retreated westward to at least the lake border moraine with the lake michigan lobe absent to impede flow drainage from the ckrv proceeded southwesterly until draining into glacial lake chicago near st joseph michigan the outburst originated from a system of saginaw tunnel channels that display convex up flow profiles and contain eskers meltwater drainage transitioned from subglacial to ice marginal and proglacial environments during the interval represented by the outburst the saginaw lobe appears to have been in a relatively stationary position

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

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

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

late wisconsinan drift stratigraphy of the saginaw ice lobe in south central michigan clay mineral analyses have been used to define two late wisconsinan till sheets of the saginaw lobe in southwestern michigan bedford till can be traced along the ground surface from the lansing moraine southward to exposures within the kalamazoo moraine and fulton till can be traced in the subsurface southward from the lansing moraine through a series of bore holes to exposures within the tekonsha moraine both tills are sometimes separated by a layer of sand and gravel the presence of sand and gravel between the bedford and fulton tills further suggests that a significant retreat 60 km of the saginaw lobe occurred between the formation of the tekonsha and kalamazoo moraines morpho stratigraphic correlations between moraines of the saginaw and huron erie lobes suggest that the interval between the deposition of the bedford and fulton tills is probably time equivalent to the erie interstade correlations between moraines of the lake michigan and saginaw lobes in southwestern michigan also suggest that the erie interstade occurred in the lake michigan lobe between the deposition of ganges and saugatuck tills

a numerical investigation of ice lobe permafrost interaction around the southern laurentide ice sheet permafrost existed around and under marginal parts of the southern laurentide ice sheet during the last glacial maximum the presence of permafrost was important in determining the extent form and dynamics of ice lobes and the landforms they produced because of influences on resistance to basal motion and subglacial hydrology we develop a two dimensional time dependent model of permafrost and glacier ice dynamics along a flowline to examine i the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology and ii the influence of permafrost on ice motion and surface profile the model is applied to the green bay lobe which terminated near madison wisconsin during the last glacial maximum simulations of ice advance over permafrost indicate that the bed upstream of the ice sheet margin was frozen for 60 200 km at the glacial maximum permafrost remained for centuries to a few thousand years under advancing ice and penetrated sufficiently deep tens of meters into the underlying aquifer that drainage of basal meltwater became inefficient likely resulting in water storage beneath the glacier our results highlight the influence of permafrost on subglacial conditions even though uncertainties in boundary conditions such as climate exist

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

variations in late cenozoic recent strike slip and oblique extensional geometries within indochina the influence of pre existing fabrics abstract from yunnan to northern thailand late cenozoic recent faults strike predominantly nne ssw n s to nne ssw and ne sw to ene wsw associated sedimentary basins are aligned ne sw to n s the regional fault patterns are commonly interpreted as strike slip dominated deformation throughout the area releasing bend and en echelon stepping patterns on faults bounding sedimentary basins indicate sinistral displacement on ne sw to ene wsw trending faults yet in the escape tectonics model left lateral displacement on the ne sw to ene wsw faults is thought to have occurred late in the miocene whilst earlier motion was dextral however in yunnan the ne sw shmax direction required for dextral motion on the n s sagaing nanting and gaoligong fault zones is consistent with sinistral motion on ene wsw striking faults which is still their sense of motion today in northern thailand the dextral sinistral switch model during the miocene is not tenable because the fang basin is of late oligocene pliocene age and requires similar age sinistral motion on the ene wsw mae chan fault in order to have opened in an alternative model northern thailand is interpreted to have evolved predominantly by oblique extension the golden triangle area marks a transition from transtensional deformation in the north to oblique extension in the south the activation of pre existing fabrics strongly affects both strike slip and extensional faults and has given rise to the similar extensional and strike slip fault patterns multiple episodes of basin inversion in northern thailand during the miocene require short term changes in stress pattern to produce the inferred changes in stress pattern it is suggested that stresses radiating out from the himalayan syntaxis exert a strong influence but were not the only important forces acting on the region

analogue modelling of multiphase rift systems abstract analogue models of multiphase rift systems show that structures produced by the first phase of extension exertsignificant control on the geometries of the later phase extensional faults two experimental series series 1 and series 2 used different modelling media subjected to two phases of extension series 1 models used a simple homogeneous sandpack whereas series 2 models used a sand polymer multilayer in each series kinematic scenarios included orthogonal extension followed by oblique extension or vice versa extension directions for oblique rift kinematics varied from 75 to 30 to the axis of rifting in all models where oblique rifting superseded earlier orthogonal rift structures the second deformation phase produced segmented fault systems and reorientation of fault tips into high angles with respect to the extension vector higher angles of obliquity resulted in increased fault segmentation orthogonal extension superposed on earlier oblique rifting leads to coalescence of segmented faults although remnants of the inherited initial rift structure remained even for low angles of obliquity the sand polymer multilayer models produced more complex fault patterns than those in the simple homogeneous sandpack showing the possible complexities that can be generated during polyphase rifting persistent first phase rift faults caused boundary fault segmentation and salients and embayments along the boundary faults during the second deformation phase the natural occurrence of similar structural styles particularly in map view may indicate that previously unrecognised multiphase rifting has occurred in these natural examples

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

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

structural development of the mid tertiary doi suthep metamorphic complex and western chiang mai basin northern thailand abstract the northern western ranges of thailand contain mylonitic gneisses of the doi suthep metamorphic complex dsmc near chiang mai mylonitic foliations outline a southeast trending dome and stretching lineations trend n80 w low grade metasedimentary rocks and tertiary fanglomerates flank the dome on the east and widespread chloritic breccia marks the intervening doi suthep detachment fault we interpret that the metamorphic complex developed between triassic and early miocene with detachment faulting mylonitization and uplift during oligocene to miocene within the dsmc dikes of mutually cross cutting hence coeval granitic pegmatite and aplite cut mylonitic orthogneiss although the contacts of the dikes are sharp the dikes contain a mylonitic fabric that parallels the fabric in the surrounding mylonitic orthogneiss thus we infer that intrusion occurred during mylonitization east of doi suthep tertiary fanglomerates of the mae rim formation overlie the doi suthep detachment fault variable strikes with dips of 10 50 and several outcrop scale fold hinges suggest that the mae rim formation is deformed into a set of non cylindrical folds numerous variably striking high angle normal faults suggest either multiple deformations or deformation in a three dimensional strain field the discovery of an intraformational angular unconformity confirms that the mae rim formation accumulated during folding

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

sedimentary and stratigraphic evidence for subglacial flooding south central michigan usa abstract the glacial landscape in south central michigan is a dissected surface with streamlined residual and upland blocks surrounded by lowland valleys dominated by outwash the upland surface has ridges hills and hummocks composed of boulder gravel which are transitional to drumlins in a down ice direction and is dissected by tunnel channels with eskers within them sedimentary descriptions from 14 gravel pits indicate a consistent stratigraphy across a width of 15 km the upland consists of bedrock covered by a lower till with subglacial melt out or lodgment characteristics above the lower till is a sand and gravel facies that passes upward into a boulder gravel facies nestled within depressions on the boulder gravel surface is a discontinuous facies of laminated sand and silt above the gravel is an upper till with supraglacial melt out and flow till characteristics analyses of the till and gravel indicate an upward change in clast lithology from locally derived carbonates to clastics and finally to crystallines from the lower till through the gravel facies into the upper till the transition mimics the bedrock lithology up ice of the study area and is explained by meltwater erosion of bedrock previously deposited subglacial sediment and overlying debris rich basal ice the systematic change in clast lithology and the stratigraphic position of the gravel facies between a subglacial and supraglacial till strongly suggests that the gravel facies sediment was deposited subglacially and that the entire till gravel till sequence resulted from the same glacial advance

comments on paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event by clarke et al quaternary science reviews 23 2004 389 407

fault zone development and strain partitioning in an extensional strike slip duplex a case study from the mesozoic atacama fault system northern chile abstract upper crustal strike slip duplexes provide an excellent opportunity to address the fundamental question of fault zone development and strain partitioning in an evolving system detailed field mapping of the mesozoic atacama fault system in the coastal cordillera of northern chile documents the progressive development of second and third order faults forming a duplex at a dilational jog between two overstepping master faults the sinistral strike slip nnw striking jorgillo and bolfin faults these are constituted by a meter wide core of foliated s c ultracataclasite and cataclasite flanked by a damage zone of protocataclasite splay faults and veins lateral separation of markers along master faults is on the order of a few kilometers second order nw striking oblique slip subsidiary fault zones do not show foliated ultracataclasite lateral sinistral separations are in the range of 10 to 200 m with a relatively minor normal dip slip component in turn third order east west striking normal faults exhibit centimetric displacement oblique slip sinistral normal fault zones located at the southern termination of the bolfin fault form a well developed imbricate fan structure they exhibit a relatively simple architecture of extensional and extensional shear fractures bound by low displacement shear fractures kinematic analysis of fault slip data from mesoscopic faults within the duplex area document that the nw striking and the ew striking faults accommodate transtension and extension respectively examination of master and subsidiary faults of the duplex indicates a strong correlation between total displacement and internal fault structure faults started from arrays of en echelon extensional extensional shear fractures that then coalesced into throughgoing strike slip faults further displacement leads to the formation of discrete bands of cataclasite and ultracataclasite that take up a significant part of the total displacement we interpret that the duplex formed by progressive linkage of horsetail like structures at the southern tip of the bolfin fault that joined splay faults coming from the jorgillo and coloso faults the geometry and kinematics of faults is compared with that observed in analog models to gain an insight into the kinematic processes leading to complex strike slip fault zones in the upper crust

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

saginaw lobe tunnel channels laurentide ice sheet and their significance in south central michigan usa abstract a network of tunnel channels in southern michigan records substantial subglacial meltwater activity beneath the saginaw lobe of the laurentide ice sheet the channels are incompletely filled with outwash contain eskers and in many places crosscut and continue beyond upland ridges previously mapped as recessional moraines the presence of the tunnel channels and drumlins on these upland ridges indicate that the ridges are not recessional moraines instead outwash fans and minor ridges record deglaciation in the area a palimpsest relationship between buried bedrock valleys and tunnel channels records the presence of multiple generations of tunnel channels evidence for a subglacial meltwater sheetflow consists of sheets of boulder gravel in upland 15 km wide with a hummocky upper surface the hummocks transform down flow into erosional remnant drumlins possibly the result of flow acceleration on a negative slope tunnel channels at the distal end of the drumlin swarm suggest collapse of the sheetflow into a channelized flow the tunnel channels then end at the sturgis moraine at the heads of large outwash fans the observed geomorphic relationships between tunnel channels moraines and drumlins in south central michigan are applicable to glacial landform studies elsewhere and indicate the important role of meltwater in landscape evolution

fast flow of the lake michigan lobe evidence from sediment landform assemblages in southwestern michigan usa abstract the dynamics of the late wisconsin lake michigan lobe of the laurentide ice sheet as interpreted by sediment landform assemblages along its southeastern margin are consistent with fast flow driven by high subglacial pore pressures a major advance of the lake michigan lobe terminated at the kalamazoo moraine where proglacial glaciotectonic activity marginal stagnation and release of subglacial meltwater marked the extent of the advance a large portion of the valparaiso moraine west of the kalamazoo moraine is actually a drumlinized till capped upland plain rather than an ice marginal landform assemblage lacustrine sediment underlying the surficial diamicton in the valparaiso upland is glaciotectonically deformed to a depth of 10 m the deformed interval consists of folded sandy and silty lacustrine sediment which is in places sharply truncated by the overlying diamicton decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton and by the sharp truncation of deformed lacustrine sediment the association of drumlins proglacial and subglacial deformation marginal stagnation and major ice marginal outwash fan deposition are indicative of fast flow perhaps in a surge these characteristics are consistent with a terrestrial ice stream model for the lake michigan lobe

on the formation of large subglacial lakes the role of subglacial water storage beneath continental ice sheets is investigated primarily for a deformable bed subglacial ponding is shown to occur under most regions of warm based ice sheets and large subglacial lakes can become established for example in the hudson bay basin the formation of large lakes depends upon the fact that the ice surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice surface gradient and increased subglacial ponding subglacial ponding likely played a large role in determining the ice sheet topography during late deglaciation and in speeding up the deglaciation process

the origin of the western lake erie grooves ohio implications for reconstructing the subglacial hydrology of the great lakes sector of the laurentide ice sheet abstract streamlined grooves and s forms cover the western lake erie islands ohio as well as the channels between the islands and the adjacent mainland although previous interpretations advocate direct glacial ice erosion we offer the alternative interpretation that forms were eroded by meltwater specifically by plucking sediment abrasion and cavitation in high velocity sediment laden flows we base our arguments on detailed descriptions and interpretations of the glacial grooves state memorial site ggsm on kelleys island the site consists of a linear furrow that is adorned by s forms in its base and on its walls these include linear forms cavettos sichelwannen comma forms multi troughed forms and plunging forms all s form sites provide a snapshot of the last phase of erosion after evolution of the local landscape through multiple generations of s form formation as s forms are found on topographic highs and lows we believe they represent a regional flow that overtopped the majority of the islands flow was initially as a sheet that quickly collapsed into channelized flow that was diverged around the islands we also believe that this flow had a major impact on the laurentide ice sheet in this region resulting in rapid glacial advance and extremely low ice sheet profiles

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

the grayling fingers region of michigan soils sedimentology stratigraphy and geomorphic development abstract this paper provides data on the landforms soils and sediments within a unique northern michigan landscape known as the grayling fingers and evaluates these data to develop various scenarios for the geomorphic development of this region composed of several large flat topped ridges that trend n s the physiography of the fingers resembles a hand previously interpreted as remnant moraines the grayling fingers are actually a pleistocene constructional landscape that was later deeply incised by glacial meltwater the sediments that comprise the fingers form a generally planar assemblage with thick 100 m sandy glacial outwash forming the lowest unit above the outwash are several meters of till that is remarkably similar in texture to the outwash below thus the region is best described as an incised ground moraine finally a thin silty cap is preserved on the flattest most stable uplands this sediment package and the physiography of the fingers are suggestive of geomorphic processes not previously envisioned for michigan although precise dates are lacking we nonetheless present possible sequences of geomorphic sedimentologic processes for the fingers this area was probably a topographic high prior to the advance of marine isotope stage 2 woodfordian ice much of the glacial outwash in the fingers is probably associated with a stagnant early woodfordian ice margin implying that this interlobate area remained ice free and ice marginal for long periods during stage 2 woodfordian ice eventually covered the region and deposited 5 10 m of sandy basal till over the proglacial outwash plain small stream valleys on the outwash surface were palimpsested onto the till surface as the ice retreated as kettle chains and as dry upland valleys the larger of these valleys were so deeply incised by meltwater that they formed the large through flowing finger valleys the silt cap that occupies stable uplands was probably imported into the region while still glaciated the fingers region a col on the ice surface could have acted as a collection basin for silts brought in as loess or in superglacial meltwater this sediment was let down as the ice melted and preserved only on certain geomorphically stable and fluvially isolated locations this study demonstrates that the impact of woodfordian ice in this region was mostly erosional and suggests that mississippi valley loess may have indirectly impacted this region

changes in beach gravel lithology caused by anthropogenic activities along the southern coast of lake michigan usa the southern coast of lake michigan is the most urbanized and most densely populated area in the great lakes region development of steel mills harbors and municipalities in nw indiana and in ne illinois in the last century and a half altered the nearshore environment so much that native beach gravel 8 mm now exist only in the exhumed paleo beach remnants from the nipissing phase 4 500 years ago of lake michigan native gravel collected from paleo beach remnants at mount baldy dune and beach house blowout contain predominantly beach shingle very platy siltstones 71 78 with secondary crystalline pebbles 18 in the east and carbonate pebbles 12 in the west a large amount of anthropogenic fill steel industry waste waste from power generating plants construction debris railroad and road fill has been added since the late 1800s to fill lake michigan and expand industrial land four areas of major coastal structures michigan city pier and breakwater burns harbor pier and breakwater gary works pier and indiana harbor peninsula altered the natural littoral drift and created four independent sectors on indiana s coast northeastern eastern central and western between which no natural transfers of coarse sediments occur downdrift from the coastal structures severe beach erosion has prompted extensive beach nourishment with non native sandy gravel four distinct populations of modern beach gravel now exist along indiana s coast of lake michigan 1 native gravel with diluted beach nourishment influence 2 native gravel with a minor industrial influence 3 compact gravel of nourished origin and 4 anthropogenic gravel of industrial origin native gravel with diluted nourishment influence is found in the western downdrift areas of the northeastern from long beach to washington park beach and eastern sectors from eastern indiana dunes state park to western dune acres and contains up to 40 compact carbonate and crystalline pebbles in addition to native beach shingle native gravel with minor industrial influence is found in the central sector of indiana s coast from central ogden dunes to marquette beach and contains predominantly beach shingle platy clastic lithology but also up to 30 of chert and other pebbles released by industry compact gravel of nourished origin contains 60 90 of carbonate and crystalline pebbles and is found in the eastern updrift areas of the northeastern michiana beach and duneland beach and eastern sectors from crescent beach to the western beverly shores anthropogenic gravel of industrial origin contains 70 90 compact chert and slag and is found in every beach of the western sector and in the westernmost beach of the central sector streams draining into southern lake michigan generally contain little coarse sediment except in their channels near the roads and railroads where angular to subangular anthropogenic pebbles predominate 70 90 however streams have very little influence on gravel lithology along the coast because they seldom discharge anthropogenic gravel into lake michigan recent changes in gravel lithology along the southern lake michigan coast may affect changes in nearshore benthic flora and fauna as well as algal and bacterial blooms during warm summer months

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

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

the kinematic history of the khlong marui and ranong faults southern thailand abstract the khlong marui fault kmf and ranong fault rf are major nne trending strike slip faults which dissect peninsular thailand they have been assumed to be conjugate to the nw trending three pagodas fault tpf and mae ping fault mpf in northern thailand which experienced a diachronous reversal in shear sense during india eurasia collision it follows that the kmf and rf are expected to show the opposite shear sense and a slip sense reversal at a similar time to the tpf and mpf new field data from the kmf and rf reveal two phases of ductile dextral shear separated by campanian magmatism paleocene to eocene post kinematic granites date the end of this phase while a brittle sinistral phase deforms the granites and has exhumed the ductile fault rocks the timing of these movements precludes formation of the faults in response to himalayan extrusion tectonics instead they formed near the southern margin of a late cretaceous paleocene orogen and may have been influenced by variations in the rate of subduction ahead of india and australia north south compression prior to reactivation of the subduction zone around southern sundaland in the eocene caused widespread deformation in the over riding plate including sinistral transpression on the kmf and rf

rhythmic till sedimentation evidence for repeated hydraulic lifting of a stagnant ice mass the youngest sedimentary facies exposed in erosional hummocky terrain in south central alberta canada is composed of alternating beds of massive silty clay diamicton and sorted sand and or silt diamicton beds are similar in thickness 5 20 cm both laterally and vertically within the sequence and sedimentary structures and consistent clast orientations support a subglacial origin for both the diamicton and the sorted sediment alternation between diamicton and sorted strata document rhythmic sedimentary sequences deposition of melt out till followed by current deposition laterally extensive sorted beds indicate that the currents responsible for sand and silt deposition must have flowed as a sheet this flow was shallow no more than 20 cm indicated by scours below boulders that were suspended from the base of glacial ice sheet flow requires that the water was stored beneath the ice prior to drainage consequently some of the diamicton may have been deposited by rain out through the shallow stored water and hence each diamicton bed may represent a combination of direct melt out onto the bed and rain out through the water column inferred cycles of water accumulation and drainage may have been annual

fabric pattern in a basal till succession and its significance for reconstructing subglacial processes abstract fabric data from a 2 5 m thick basal till succession in kurzetnik poland consisting of three structurally distinct till units including a deformation till were examined to test whether different processes of deposition and deformation as indicated by till structure are reflected in the till fabric pattern surprisingly throughout the succession the till fabric is unidirectional and very highly clustered mean s1 0 876 and standard fabric interpretation methods including binary and triangular diagrams failed to differentiate between the three units and constrain the origin of the till facies it is shown that the a axis length as well as the ratio between a b and a c axes has no effect on the fabric strength and there is no correlation between the fabric strength and clast size within the 0 7 5 6 cm grain size range the bootstrapping method applied to test the statistical significance of variance shows that 1 some variations in the fabric strength within the same till facies are due to the sampling effect while other variations can be interpreted as true effects of strain and 2 fabric strength may vary significantly over very short distances within the same till facies very high fabric strength in the deformation till is inconsistent with a model of weak to moderate fabric strength resulting from penetrative deformation supporting the theory that subglacial deforming tills behave as coulomb plastic rather than viscous materials

successive subglacial depositional processes as interpreted from basal tills in the lower vistula valley n poland abstract three basal till facies from the lower vistula valley were examined the lowest facies a sandy diamicton with characteristic sand inclusions forming detached and attenuated folds is overlain by a bedded till characterized by alternating diamictons and sorted sediment layers the uppermost till facies is a homogeneous diamicton the three till facies must have been formed by complex subglacial sedimentary processes during the first late weichselian ice advance the lowest till facies is interpreted as a deformation till and accumulated during the initial stage of the ice advance the middle facies represents a stagnation phase during the initial ice advance and was deposited during recurrent periods of subglacial melt out followed by meltwater sedimentation the upper till facies was deposited by direct subglacial melt out during a stage of stagnant ice it is suggested that bed deformation and temporarily enhanced basal sliding have been caused by ice streaming at the time of the ice sheet advance and just before its stagnation

the sediment infill of subglacial meltwater channels on the west antarctic continental shelf subglacial meltwater plays a significant yet poorly understood role in the dynamics of the antarctic ice sheets here we present new swath bathymetry from the western amundsen sea embayment west antarctica showing meltwater channels eroded into acoustic basement their morphological characteristics and size are consistent with incision by subglacial meltwater to understand how and when these channels formed we have investigated the infill of three channels diamictons deposited beneath or proximal to an expanded grounded west antarctic ice sheet are present in two of the channels and these are overlain by glaciomarine sediments deposited after deglaciation the sediment core from the third channel recovered a turbidite sequence also deposited after the last deglaciation the presence of deformation till at one core site and the absence of typical meltwater deposits e g sorted sands and gravels in all three cores suggest that channel incision pre dates overriding by fast flowing grounded ice during the last glacial period given the overall scale of the channels and their incision into bedrock it is likely that the channels formed over multiple glaciations possibly since the miocene and have been reoccupied on several occasions this also implies that the channels have survived numerous advances and retreats of grounded ice

the kankakee torrent and other large meltwater flooding events during the last deglaciation illinois usa abstract evidence of the kankakee torrent ekblaw and athy 1925 includes boulder bars formed on a scoured bedrock surface west of kankakee illinois and overflow channels that connect several moraine dammed basins wauponsee watseka and pontiac willman and payne 1942 geomorphic evidence of a large scale flood event in the illinois valley includes features such as erosional residuals hajic 1990 the age of the kankakee torrent is about 19 000 cal yr bp based on the pooled mean of four radiocarbon ages of tundra plant stems and leaves from the oswego channel complex median probability 18 930 cal yr bp 1 range 18 870 18 970 cal yr bp analysis of recently obtained sediment cores from the middle illinois river valley near havana illinois has revealed the bedrock surface is defended by a mantle of bouldery debris buried by 15 m of mostly slackwater lake sediment radiocarbon ages of needles archived in the lake sediment reveal evidence for an early lake phase that post dates the kankakee torrent 18 030 17 530 cal yr bp and a later lake phase 15 690 13 040 cal yr bp the radiocarbon ages indicate that the deeply buried bouldery rubble was deposited by the kankakee torrent consideration of isostasy indicates that the earlier lake phase at havana may have been associated with downward flexure of land surface in response to glacier loading the younger lake phase was caused in part by deposition of a sediment dam the savanna deer plain terrace at the mouth of the illinois river the lake shoaled due to passing of the isostatic forebulge across the area

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

glacigenic clast fabrics genetic fingerprint or wishful thinking the interpretation of glacigenic diamictons is a subjective process for which quantitative support is frequently sought from parameters such as clast shape and fabric it has been widely suggested that different glacigenic diamicton facies possess distinct clast fabric signatures this paper examines this concept using a data set of 111 clast fabrics and a synthesis of published results eigenvalues are calculated and compared for a variety sedimentary facies it is concluded that clast fabric alone is not able to discriminate between different glacigenic facies and it is argued that clast fabric offers little quantitative support in the interpretation of glacigenic sediments it is suggested therefore that although clast fabric may continue to have a role as an indicator of relative strain at specific sites its use in the discrimination of glacigenic facies is limited consequently we should be much more selective in undertaking such analyses in the future copyright 1999 john wiley sons ltd

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

subglacial water sheet floods drumlins and ice sheet lobes the effect of subglacial lakes upon ice sheet topography and the velocity patterns of subglacial water sheet floods is investigated a subglacial lake in the combined michigan green bay basin great lakes north america leads to 1 an ice sheet lobe in the lee of lake michigan 2 a change in orientations offlood velocities across the site of a supraglacial trough aligned closely with green bay in agreement with drumlin orientations 3 low water velocities in the lee of lake michigan where drumlins are absent and 4 drumlinization occurring in regions of predicted high water velocities the extraordinary divergence of drumlin orientations near lake ontario is explained by the presence of subglacial lakes in the ontario and erie basins along with ice sheet displacements of up to 30 km in eastern lake ontario the megagrooves on the islands in western lake erie are likely to be the product of the late stage of a water sheet flood when outflow from eastern lake ontario was dammed by displaced ice and instead flowed westward along the erie basin the finger lakes of northern new york state northeastern u s a occur in a region of likely ice sheet grounding where water sheets became channelized green bay and grand traverse bay are probably the products of erosion along paths of strongly convergent water sheet flow

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

glacial lake spillway incision and deposition of a coarse grained fan near watrous saskatchewan the watrous spillway was rapidly incised during a short lived outburst from glacial lake elstow in its outlet area the bed of lake elstow was composed of stagnant ice the 40 km long spillway is

meltwater intensive glacial retreat in polar environments and investigation of associated sediments example from pine island bay west antarctica abstract modern pine island and thwaites glaciers which both drain into pine island bay are among the fastest changing portions of the cryosphere and the least stable ice streams in antarctica here we show that the uppermost sediment unit in pine island bay was deposited from a meltwater plume a plumite during the late stages of ice sheet retreat 7 8 6 k cal yr bp and argue that this deposit records episodes of meltwater intensive sedimentation the plumite is a hydraulically sorted glacially sourced draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line the uppermost sediment unit is interpreted as a product of non steady state processes in which low background sedimentation in large bedrock carved basins alternates with episodic purging of sediment laden water from these basins the inner part of pine island bay contains several basins that are linked by channels with a storage capacity on the order of 70 km 3 of stagnant water and significant sediment storage capacity purging of these basins is caused by changes in hydraulic potential and glacial reorganization the sediment mobilized by these processes is found here to total 120 km 3 this study demonstrates that episodes of meltwater intensive sedimentation in pine island bay occurred at least three times in the holocene the most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit we note that the final phase of ice stream retreat in marguerite bay was marked by a similar sedimentary event and suggest that the modern thwaites glacier is poised for an analogous meltwater intensive phase of retreat

three dimensional inversion modelling of a neoproterozoic basin in the southern prince charles mountains east antarctica abstract three dimensional inversion modelling of airborne magnetic data acquired in the prince charles mountains east antarctica provides an insight into the sub ice distribution and three dimensional geometry of a neoproterozoic sedimentary basin a three dimensional starting model was created from two two dimensional gm sys modelling and our current geological understanding of the study area three dimensional vpmg inversion modelling was performed on the aeromagnetic data to obtain an acceptable fit between the observed response collected in the field and the calculated response of the three dimensional model modelling suggests that the base of the basin undulates and is relatively unstructured however the margins of the basin thicken from north 4 km to south 11 km the volume of the sodruzhestvo group that in fills the sedimentary basin has been calculated at approximately 35 000 km3 modelling of banded iron formations at the southern margin of the basin and a sharp magnetic contrast in the north reveal that both contacts dip toward the south we interpret this asymmetric geometry of the sedimentary basin as having began as a set of half grabens bounded by an underlying listric fault that flattened at depth below the sedimentary basin subsequent early palaeozoic inversion of this structure resulted in reactivation along the low angle basal detachment but rather than taking its original course underneath the sedimentary basin the fault ramped up along the southern margin this process caused exhumation of the underlying banded iron formations which are now juxtaposed at similar crustal levels to the neoproterozoic cover rocks