the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

ichnology of a paleopolar river dominated shallow marine deltaic succession in the mackellar sea the mackellar formation lower permian central transantarctic mountains antarctica abstract the lower permian mackellar formation in the beardmore glacier area of the central transantarctic mountains antarctica was deposited between 80 and 85 s paleolatitude previous studies suggest that mackellar formation strata were deposited in either a large glacial lake or inland sea our study identified 30 ichnogenera from turnabout ridge and buckley island of which 1 none are exclusively freshwater forms 2 20 ichnogenera are found in freshwater brackish and marine settings and 3 10 ichnogenera are exclusively found in marine settings combining ichnologic evidence with sedimentologic observations suggests that the mackellar formation was deposited in a river dominated delta in a fully marine to brackish marine setting trace fossil associations are grouped into the arenicolites phycodes lingulichnus arenicolites planolites kouphichnium phycodes teichichnus arenicolites and planolites teichichnus phycodes ichnocoenoses of a mixed skolithos cruziana ichnofacies these associations are characteristic of epi and endobenthic worms arthropods and mollusks with the vast majority of the traces being diminutive in diameter and length and exhibit shallow 10 mm penetration depths these ichnocoenoses occur in paleoenvironments that include the prodelta distal to proximal delta front including mouth bars and subaqueous terminal distributary channels the diminutive morphology shallow penetration depth low bed ichnodiversity high overall ichnodiversity and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short lived communities composed of small bodied organisms stressed by high freshwater input and high sedimentation rates

on the origin of the itarare group basal nonconformity and its implications for the late paleozoic glaciation in the parana basin brazil abstract outcrop studies of the itarare group in the alfredo wagner area along the eastern margin of the parana basin in brazil reveal a partially exhumed nnw sse oriented glacial paleovalley the carboniferous rio do sul formation represents the basal interval of the glacially influenced itarare group and rests directly on precambrian basement rocks this nonconformity is thought to represent an areal scouring surface as indicated by the series of glacially carved linear depressions that were incised into the glaciated bedrock during glacial advances these large scale erosional landforms differ in their extent by orders of magnitude and include wide deep troughs as well as narrower shallower gouges glacial troughs and gouges usually display smaller scale subglacial erosion landforms such as polished and grooved striations on their walls and floors these indicate the nnw motion of a warm based grounded glacier in addition large scale erosional features represent local topographic lows within the major glacial paleovalley these local lows are large enough to contain part of the succeeding deglacial deposits which thin toward and onlap the wall of these depressions we grouped these deglacial deposits into six genetic facies associations fa 1 to 6 within three fining upward glacial cycles fa 1 is composed of black shale and represents an initial marine flooding event it can be correlated with the regionally widespread lontras shale fa 2 is composed of sandstones and mudstones associated with flood derived hyperpycnal flows and occasionally with surge type turbidites fa 3 is represented by plastered or injected matrix supported conglomerates emplaced as lodgment tills fa 4 comprises matrix and clast supported conglomerates sandstones and mudstones attributed to ice rafting and concentrated flows in grounding line fan facies this unit also contains ice keel dragging features carved into soft substrate fa 5 is composed of dropstone bearing black shale related to a second major marine flooding event within the paleovalley fa 6 comprises sandstones associated with channelized surge type turbidites forming the second turbidite system in the succession as these deposits are confined to a paleovalley we infer that sedimentation was influenced by topographically controlled ice streams instead of non confined widespread ice lobes as previously suggested reconstructing south america and southern africa in their positions during the lpia suggests that the glacial valleys then present in the namibia area may have extended further into the eastern margin of the parana basin in this scenario confined outlet glaciers would have flowed out from the namibian windhoek ice cap and terminated along the eastern margin of the parana basin

glaciation and tectonics in an active intracratonic basin the late palaeozoic itarare group parana basin brazil the parana basin 1 600 000 km2 is the largest intracratonic basin in southern south america and contains a thick 1300 m permo carboniferous glacial succession the itarare group this paper describes over 1700 m of drill core recovered during recent exploration for oil and gas itarare group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones and massive and laminated mudstones facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin three stratigraphic formations can be defined across the basin each consisting of a lowermost sandstone rich member overlain by a diamictite rich member examination of itarare group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the itarare group ice masses fringing the eastern southern african and western bolivian basin margins supplied sediment to the basin in the form of fluvio glacial deltas fans and floating ice tongues this sediment was then resedimented downslope as debris flows and turbidites both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step wise expansion by outward faulting within late proterozoic mobile belts the position of successive basin margins can be related to specific lineament structures in the underlying basement asymmetric expansion of the parana basin occurred along the northern and southern basin margins during deposition of the itarare group this expansion probably reflects shallow crustal adjustments activated by collisional movements along the andean margin of south america during the hercynian orogeny

development of the accretionary prism along peru and material flux after subduction of nazca ridge results from ocean drilling program leg 112 indicated tectonic erosion of the peruvian convergent margin during subduction of the nazca ridge followed by renewed accretion against the erosional scar seismic images and swath mapping morphology show a regional geology shaped as subduction of nazca ridge migrated 800 km along the peru trench the accretionary prism is imaged at two stages of development since upper miocene time with depth migrated seismic records in which the back stop is well defined from these data material flux can be quantified after the ridge crest subducted and accretion dominated over erosion the prism grew rapidly to 10 to 15 km width during rapid growth the margin taper was large and about 60 percent of the sediment supply accreted as the prism growth slowed only 30 percent accreted despite an increased trench sediment supply since the convergence rate changed little the inverse relation between sediment supply and prism growth rate suggests that other processes allow most of the sediment input to be subducted the decreased prism growth may be partially controlled by varying the structure of the back stop the force required to activate faults cutting across the back stop is probably greater than the force allowed by basal friction across the plate boundary thus the shear stress transmitted across the plate boundary is insufficient to drive out of sequence thrust faults that would thicken the back stop or raise it beyond a limited height a constant back stop height limits accretion and the subduction window appears to open and accommodate increased trench sediment beneath the back stop rather than inducing a transport of sediment over the top of the back stop nazca ridge subduction affected the convergent margin mass flux for about 8 ma mass balancing indicates an order of magnitude increase in the current sediment volume subducted in the north compared to that near the ridge crest when growth of the accretionary prism slowed a greater terrigenous input through the trench was accommodated by sediment subduction the resulting range of material flux is estimated to increase the sediment interlayer between the plates about 500 m which may affect coupling

glacial advance and retreat sequences in a permo carboniferous section central transantarctic mountains episodes of glacial advance and retreat can be recognized through analysis of vertical facies sequences in the permo carboniferous pagoda formation of the beardmore glacier area antarctica the formation includes a remarkably complete record of continental sedimentation near the terminus of a temperate glacier facies sequence is pre eminent for inferring glacial advance and retreat other important criteria are abundance and geometry of sandstone interbedded with diamictite diamictite character and nature of bed contacts using these characteristics advance and retreat sequences 5 60 m thick are recognized a sharp contact with a striated surface and erosional relief overlain by structureless diamictite lodgement till is typical of grounded ice advance grounded ice retreat is characterized by structureless diamictite lodgement till overlain by crudely stratified diamictite melt out till and then by diamictite interbedded with sandstone and conglomerate flow till and glacio fluvial or glacio lacustrine deposits gradational contacts between shale overlain by diamictite and diamictite overlain by shale characterize advance and retreat respectively in subaqueous settings pauses in sediment accumulation minor fluctuations of the ice margin and or changes in subglacial dynamics are indicated by specific features within diamictite units such as probable frost wedge casts single layer boulder beds sharp sedimentary contacts and changes in diamictite character these minor events are superimposed upon the main advance retreat cycles study of both the overall facies sequence and of individual diagnostic structures albeit in an incomplete stratigraphic record permits a distinction between major and minor advance retreat events as many as six major advance retreat cycles exist in some pagoda sections but the number of cycles present varies in different sections

proglacial deposition and deformation in the upper carboniferous to lower permian wynyard formation tasmania a process analysis abstract the wynyard formation of tasmania australia provides the youngest evidence of grounded ice during the late carboniferous early permian in the tasmania basin of southeastern gondwana during the late paleozoic ice age within the wynyard formation four facies associations are recognized 1 massive diamictite 2 stratified diamictite 3 conglomerate and sandstone and 4 deformed mudstone and fine sandstone a detailed facies analysis was performed in order to interpret the depositional processes and environments the massive diamictite facies association contains massive diamictite and sandstone and was deposited primarily by iceberg rain out in a subaqueous morainal bank setting the stratified diamictite facies association is composed of stratified diamictite sandstone and conglomerate and was deposited by debris flows and iceberg rain out and deformed by glacial pushing the conglomerate and sandstone facies association is made up of cross stratified channelized conglomerate and pebbly sandstone that were deposited by glacial outwash on grounding line fans the deformed mudstone and fine sandstone facies association is composed of pervasively deformed pebbly mudstone and fine grained sandstone that exhibit volcano flame and dyke structures this facies association was deposited by a combination of suspension settling iceberg rain out and soft sediment deformation in a quiet distal proglacial setting the facies analysis supports the interpretation that the wynyard formation was deposited by a wet based tidewater glacier or glaciers the depositing glacier s occupied a 40 km wide trough in northwest tasmania based on the distribution of the wynyard formation and the presence of glacial deposits in other eroded troughs in tasmania glaciation occurred in the region within broadly eroded valleys the wynyard formation and overlying mudstone of the inglis formation provide a glacial postglacial signature similar to those in south africa antarctica and eastern australia during the latest carboniferous early permian therefore the climate warmed in southern gondwana following this glacial interval the continued glaciation in eastern australia was a result of regional topography and oceanographic processes

processes and products of grounding line fans from the permian pagoda formation antarctica insight into glacigenic conditions in polar gondwana abstract glacimarine grounding line fans are subaqueous depositional features that form due to the expulsion of sediment laden subglacial waters at the grounding lines of temperate tidewater glaciers few studies of ancient grounding line fans exist this study describes and interprets several ancient glacimarine grounding line fans and their physical characteristics using the lower permian pagoda formation along tillite glacier in the central transantarctic mountains antarctica as a deep time example wedge shaped sandstone bodies are used to identify major depositional processes and products that occurred during fan formation the depositing processes on these fans operated in tandem as tractive freshwater discharge from beneath the glacier s was progressively replaced down the fans in the direction of flow by buoyant upwelling and the development of overflow plumes tractive flow deposits are characterized by trough and climbing cross stratification while deposits resulting from settling from meltwater plumes consist of horizontal laminations and abundant soft sediment deformational structures load flame and diapiric structures secondary features such as thrust and normal faults resulted from advance and retreat dynamics of the ice front whereas mass flow deposits convolute bedding recumbent and s shaped folds slumps and slides resulted from resedimentation because glacimarine grounding line fans require specific depositional conditions to develop their identification is useful in constraining environmental conditions in the rock record for the pagoda formation the occurrence of grounding line fan deposits is significant as these strata were originally interpreted as deposits of a large terrestrial ice sheet centered over the location of the present transantarctic mountains that extended outward and covered much of gondwana for up to 90 million years however this study demonstrates that these rocks were deposited in a glacimarine setting results combined with other recent studies suggest that multiple small temperate ice sheets occurred in south polar antarctica during the late paleozoic ice age rather than a single massive ice sheet

subaqueous outwash fan and esker sandstones in the permo carboniferous dwyka formation of south africa abstract four sandstone facies were defined in a 300 m thick diamictite member of the glacigene permo carboniferous dwyka formation the laterally persistent type a sandstones comprising quartz arenite are conformable to the bedding of the diamictite and are unreformed they are interpreted as subaqueous outwash fan deposits sandstone facies b also quartz arenites occurs intermittently along bedding planes in the diamictite and shows soft sediment deformation it represents subaqueous segmented outwash fan deposits which were primarily deformed by density loading of the soft diamicton the highly irregular type c sandstones comprise quartz and lithic arenites and wackes are randomly distributed in the diamictite and are deformed they ale interpreted as esker and esker delta deposits and rafted lumps of frozen meltwater sands deformed by overriding ice or density loading of the diamicton facies d consists of quartz and lithic arenites and represents clastic dikes and diapiric injections formed by density loading of waterlogged meltwater sand the three diamictite subfacies associated with the sandstones were deposited in open water by iceberg rafting suspension settling and debris flow by a combination of lodgement and melt out processes below grounded ice and below an ice shelf by debris rain suspension settling and slope failure the outwash fan deposits esker deltas clastic dikes and diapiric injections are confined to those parts of the basin covered by open water and the ice shelf the esker deposits formed in areas overlain by grounded ice episodic advance of the ice lobes and oscillation of the ice grounding line eroded the fan sediments and also contributed to the deformation of the sand bodies

lithofacies and origin of the buckeye formation late paleozoic glacial and glaciomarine sediments ohio range transantarctic mountains antarctica up to 300 m of glaciogenic late paleozoic buckeye formation rest unconformably upon an erosional surface cut on and in places through early devonian horlick formation in the ohio range antarctica the diamictite exhibits a gradual transition upsection from direct glacial to subsequent glaciomarine deposition lowermost beds include diamictite deposited directly from grounded ice numerous striated pavements indicate paleo ice flow from west to east upsection many beds are internally stratified and this with the presence of fine laminated interbeds provides evidence of subaqueous deposition geochemical textural and paleontological data suggest a marine influence towards the top of the buckeye most diamictite horizons are horizontally stratified with a decreasing proportion of small dropstones buckeye formation is conformably overlain by discovery ridge formation beds of probable shallow marine origin

andean forearc dynamics as recorded by detrital zircon from the eocene talara basin northwest peru abstract eocene strata of the talara forearc basin of northwest peru contain detrital zircon dz populations that when integrated with other provenance indicators record paleogeographic shifts in the andean forearc that can be linked to larger scale tectonic drivers such as subduction erosion plate convergence rate and regional accretion events because forearc basins along the western margin of south america are particularly difficult to preserve the new dz results provide rare insight into the trench arc dynamics associated with the andean orogenic cycle the talara basin tapped into both the andean volcanic arc and older basement and the dz populations subsequently reflect long lived plate interactions and progressive crustal growth along the northwestern edge of amazonia gondwana and south america dominant u pb zircon age populations include 36 110 ma andes convergence 215 285 ma western gondwana extension 460 625 ma rodinia extension and western gondwana convergence 950 1250 ma grenville orogeny and 1250 ma amazonia assembly the data corroborate previous geochronology on pre andean basement and support the existence of a famatinian arc 480 ma and carboniferous triassic magmatism along northwestern gondwana pre andean and amazonian dz likely was recycled from paleozoic metasedimentary rocks of the andean cordillera and amotape terrane although the data do not preclude delivery of amazonian detritus directly into the forearc via a large scale westward drainage the andean dz population constrains the timing of arc activity and quiescence with two peaks at 75 ma and 50 ma and a gap at 70 ma linked to accretion of the caribbean oceanic plateau against northwest south america arc volcanism was concurrent with eocene forearc deposition and syndepositional dz is used to revise maximum depositional age for the upper eocene helico member and verdun formation progressive subsidence and arc shut down in the late eocene coincide with arc collision to the north uplift of the amotape block subduction erosion and slab shallowing

late paleozoic ice age glaciers shaped east antarctica landscape abstract the erosion history of antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics however because of the vast polar ice sheet covering more than 99 of antarctica land mass the continental surface response to glacial erosion remains largely unknown over the last decade the subglacial topography of antarctica has been imaged by airborne radar surveys these studies revealed high and complex sub glacial relief in the core of the east antarctic shield interpreted as resulting from rifting episodes and low long term erosion rates or repeated large scale glacial retreats and advances in east antarctica thermochronology studies have revealed a spatially localized cenozoic erosion starting after 34 ma with a maximum denudation of 2 km in the lambert trough low pre glacial erosion rates before 34 ma have been inferred since the permian period following a phase of significant 2 km erosion during the late paleozoic between 350 and 250 ma however the exact extent magnitude and significance of this late paleozoic erosion phase remain elusive here we show that homogeneous exhumation occurred at the scale of the terre adelie margin of east antarctica in response to major glacial erosion during the late paleozoic ice age lpia our data require homogeneous exhumation and 4 km erosion between 340 and 300 ma along a 600 km profile along the terre adelie george v land coast the data are inconsistent with either exhumation during permian rifting or with significant 1 5 km cenozoic glacial erosion which requires lpia glaciers to have been temperate promoting glacial sliding erosion and sediment transfer even at high latitudes unlike in the present situation

lithofacies and seismic reflection interpretation of temperate glacimarine sedimentation in tarr inlet glacier bay alaska abstract high resolution seismic reflection profiles of sediment fill within tarr inlet of glacier bay alaska show seismic facies changes with increasing distance from the glacial termini five types of seismic facies are recognized from analysis of huntec and minisparker records and seven lithofacies are determined from detailed sedimentologic study of gravity vibro and box cores and bottom grab samples lithofacies and seismic facies associations and fjordfloor morphology allow us to divide the fjord into three sedimentary environments ice proximal iceberg zone and ice distal the ice proximal environment characterized by a morainal bank depositional system can be subdivided into bank back bank core and bank front subenvironments each of which is characterized by a different depositional subsystem a bank back subsystem shows chaotic seismic facies with a mounded surface which we infer consists mainly of unsorted diamicton and poorly sorted coarse grained sediments a bank core depositional subsystem is a mixture of diamicton rubble gravel sand and mud seismic reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface a bank front depositional subsystem consists of mainly stratified and massive sand and is characterized by internal hummocky facies on seismic reflection records with significant surface relief and sediment gravity flow channels the depositional system formed in the iceberg zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt on seismic reflection profiles this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone the depositional system formed in the ice distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt this depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on huntec records

ice marginal environment and ecosystem prior to initial advance of the late palaeozoic ice sheet in the mount butters area of the central transantarctic mountains antarctica basal rocks of the upper carboniferous to lower permian pagoda formation at mount butters provide an unusual view of periglacial conditions in the central transantarctic mountains region prior to the initial advance of the gondwanide ice sheet these rocks were deposited on a high relief unconformity that developed on granite deposition within relief on the unconformity possibly in the lee of a granite buttress protected the rocks from erosion during subsequent overriding by the ice sheet the succession reflects deposition in a glacial fed to ice contact lake that contained a freshwater crustacean fauna centimetre to decimetre scale basal layers include breccia and coarse grained sandstone the occurrence of breccia resting on weathered granite suggests sedimentation as scree and as mass flow deposits overlying decimetre to metre scale stratified diamictites interbedded with metre scale coarsening upward successions of siltstone to cross laminated sandstone suggest lacustrine deposition by suspension settling rain out of ice rafted debris and deltaic progradation thin zones with abundant conchostracans and or with prolific trace fossils in addition to less common remains of other crustaceans attest to the presence of a low diversity benthic fauna conchostracans are concentrated in a series of thin beds that reflect moderately lengthy perhaps seasonal periods of free flowing water patchy vertical and lateral distribution of intense bioturbation and profuse trace fossils probably reflect repeated colonization events during times of favourable environmental conditions massive diamictite overlies the basal rocks and indicates that the ice marginal lake was subsequently overridden by the late palaeozoic ice sheet occurrences of lodgement till glacitectonite and deformation till suggest deposition from temperate or warm based ice whereas underlying lacustrine and deltaic deposits along with a crustacean and trace fossil fauna suggest temperate periglacial conditions previous studies have stressed that upper palaeozoic glacigenic deposits in antarctica and in gondwanaland record deglaciation events in contrast rocks at mt butters provide an unusual glimpse into an ice margin lake and its fauna just prior to ice sheet advance

reevaluation of the timing and extent of late paleozoic glaciation in gondwana role of the transantarctic mountains evidence from antarctica indicates that a 2000 km long section of the transantarctic mountains including victoria land the darwin glacier region and the central transantarctic mountains was not located near the center of an enormous car boniferous to early permian ice sheet as depicted in many paleo geographic reconstructions weathering profiles and soft sediment deformation immediately below the preglacial pre permian un conformity suggest an absence of ice cover during the carbonif erous otherwise multiple glacial cycles would have destroyed these features the occurrence of glaciotectonite massive and strat ified diamictite thrust sheets sandstones containing dewatering structures and lonestone bearing shales in southern victoria land and the darwin glacier region indicate that permian sedimenta tion occurred in ice marginal periglacial and or glaciomarine set tings no evidence was found that indicates the transantarctic mountains were near a glacial spreading center during the late paleozoic although these findings do not negate carboniferous glaciation in antarctica they do indicate that gondwanan glacia tion was less widespread and therefore that glacially driven changes to other earth systems i e glacioeustatic fluctuations cli mate were much smaller than previously hypothesized

evaluation of conditions along the grounding line of temperate marine glaciers an example from muir inlet glacier bay alaska abstract in the marine environment stability of the glacier terminus and the location of subglacial streams are the dominant controls on the distribution of grounding line deposits within morainal banks a morainal bank complex in muir inlet glacier bay se alaska is used to develop a model of terminus stability and location of subglacial streams along the grounding line of temperate marine glaciers this model can be used to interpret former grounding line conditions in other glacimarine settings from the facies architecture within morainal bank deposits the muir inlet morainal bank complex was deposited between 1860 a d and 1899 a d and historical observations provide a record of terminus positions glacial retreat rates and sedimentary sources these data are used to reconstruct the depositional environment and to develop a correlation between sedimentary facies and conditions along the grounding line four seismic facies identified on the high resolution seismic reflection profiles are used to interpret sedimentary facies within the morainal bank complex terminus stability is interpreted from the distribution of sedimentary facies within three distinct submarine geomorphic features a grounding line fan stratified ridges and a field of push ridges the grounding line fan was deposited along a stable terminus and is represented on seismic reflection profiles by two distinct seismic facies a proximal and a distal fan facies the proximal fan facies was deposited at the efflux of subglacial streams and indicates the location of former glacifluvial discharges into the sea stratified ridges formed as a result of the influence of a quasi stable terminus on the distribution of sedimentary facies along the grounding line a field of push ridges formed along the grounding line of an unstable terminus that completely reworked the grounding line deposits through glacitectonic deformation between 1860 a d and 1899 a d 39 years 8 96 10 8 m 3 of sediment were deposited within the muir inlet morainal bank complex at an average annual sediment accumulation rate of 2 3 10 7 m 3 a this rate represents the annual sediment production capacity of the glacier when the muir inlet drainage basin is filled with glacial ice

on the significance of diopside and oldhamite in enstatite chondrites and aubrites enstatite is the primary silicate phase of equilibrated enstatite chondrites eecs the cao contents of these enstatites lie close to or on the enstatite diopside phase boundary yet curiously diopside has always been absent from eec assemblages in contrast aubrites contain abundant diopside even though they are thought to be derived from an e chondrite like protolith a phase equilibrium analysis of the ca mg fe mn si o s system under reducing conditions solves this enigma and shows that diopside bearing eecs should commonly be found when s fugacity is sufficiently high e g fe fes buffer low o fugacity limits the stability of diopside in favor of oldhamite under such conditions the relative stability of diopside and oldhamite is described by the reaction camgsi2o6 mgs cas mg2si2o6 a large bulk compositional field exists where diopside and oldhamite are simultaneously stable the existence of oldhamite does not preclude the stability of diopside phase diagram topology demonstrates that bulk compositions lying in the enstatite oldhamite field and enstatite oldhamite alabandite field have enstatite cao contents nearly identical to that of enstatite in equilibrium with diopside alone this explains the high enstatite cao contents of all eecs that do not contain diopside this study also reports the discovery of the first eec to contain metamorphic diopside the antarctic meteorite eet 90102 elephant moraine 90102 has a typical el6 texture and contains the assemblage enstatite diopside albite kamacite troilite sinoite and graphite trace quantities of alabandite oldhamite and daubreelite are also present diopside is stable in eet 90102 because its bulk composition lies within either the enstatite diopside oldhamite alabandite or diopside alabandite enstatite stability fields in contrast all other eecs analyzed to date have bulk compositions lying in the enstatite oldhamite alabandite stability field the discovery of diopside in eet 90102 helps confirm the predictions of the phase equilibrium analysis elephant moraine 90102 experienced a high temperature metamorphic equilibration from which it was quenched the enstatite diopside cas in alabandite and fe in alabandite geothermometers yield temperatures of last equilibration of 900 c the absence of daubreelite and schreibersite along with high troilite cr contents and high kamacite p contents confirm a high temperature metamorphic quench the eet 90102 chondrite experienced a somewhat different cooling history and has a slightly different bulk composition than all other eecs studied to date however the close mineralogic petrologic and textural similarities between eet 90102 and nominal el6 chondrites signify that it should be classified as a diopside and sinoite bearing el6 chondrite assuming that the aubrites formed from an e chondrite like protolith a source rock similar to that of a diopside bearing eec offers a clear advantage for aubrite formation melting of a diopside saturated eec protolith would not require conversion of cas to achieve diopside saturation upon cooling

sediment rich meltwater plumes and ice proximal fans at the margins of modern and ancient tidewater glaciers observations and modelling turbid meltwater plumes and ice proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers however the spacing and temporal stability of these subglacial channels is poorly understood this has significant implications for understanding the geometry and distribution of quaternary and ancient ice proximal fans that can form important aquifers and hydrocarbon reservoirs remote sensing and numerical modelling techniques are applied to the 200 km long marine margin of a svalbard ice cap austfonna to quantify turbid meltwater plume distribution and predict its temporal stability results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice proximal fans plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap modelled water routing patterns are in reasonable agreement with satellite mapped plume locations however glacial retreat of several kilometres over the past 40 years has limited build up of significant ice proximal fans a single fan and moraine ridge is noted from marine geophysical surveys closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans schematic models of ice proximal deposits represent varying glacier terminus stability i stable terminus where meltwater sedimentation produces an ice proximal fan ii quasi stable terminus where glacier readvance pushes or thrusts up ice proximal deposits into a morainal bank and iii retreating terminus with short still stands allowing only small sediment lobes to build up at melt stream portals these modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient ordovician glacial system thick turbidite successions and large fans in the late ordovician suggest either high magnitude events or sustained high discharge consistent with a relatively mild palaeo glacial setting for the former north african ice sheet

dynamics of marine glacier termini read from moraine architecture allostratigraphic mapping of the internal facies architecture of marine moraines reveals the development history of ice contact sedimentary systems the new method for a high resolution analysis of the dynamic stratigraphy of moraines provides important information on the ice front behavior glacier dynamics and regional climatic conditions based on a series of case studies of the moraines of temperate glaciers in norway an allostratigraphic model is suggested as a conceptual guide for the field analysis of ice contact deposits based on outcrop sections as well as seismic or ground penetrating radar profiles

glacimarine processes at grounding line fans and their growth to ice contact deltas abstract grounding line fans originate from subglacial and basal stream tunnels at grounding lines of glaciers terminating in a marine environment during melt seasons discharge forms a turbulent jet beyond the efflux over the initial zone of flow establishment in the jet it may remain in contact with the sea floor for up to 13 4 d d tunnel diameter along a runout distance if velocity is constant plug flow in this zone deposits marine outwash sediment commonly having chaotic texture and graded and welded contacts texture may vary rapidly because of discharge pulses and the jet may move laterally to produce sheet or cut and fill geometries imbricate gravel is deposited near the efflux then farther out are sheet or weakly channelized finer grained gravels and sands in some instances a migrating barchanoid bar forms at the detachment zone and forms large scale trough cross beds beyond the detachment zone the turbulent jet becomes vertical and sediment cascades from it in a veil this sediment is added to by flows from continuous failures of bed load sediment in the detachment zone resulting deposits are interstratified sediment gravity flows and thick coarse end members of cyclopsams the jet changes to a plume when inertial forces become less than buoyancy forces turbulent vorticies within the jet can re entrain particles into a buoyant plume the plume remains vertical although continuously spreading until reaching neutral buoyancy fan depocentres have been observed to accumulate at over 10 6 m 3 a 1 in temperate glacial areas eventually at quasi stable grounding lines fans may aggrade to sea level to form ice contact deltas at incipient deltas when the delta plain is intertidal coarse sediment is redistributed to the prodelta with each tidal cycle intense prodelta rhythmites mark the transition of a fan into a delta

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

modeling glacial meltwater plume dynamics and sedimentation in high latitude fjords 1 a model sedplume has been developed to simulate marine sediment deposited by glacial meltwater plumes emerging from tidewater glaciers turbid meltwater emerging from beneath a glacier into a fjord rises as a buoyant forced plume due to density contrasts with the ambient fjord water sedplume assumes that meltwater discharge flows at a constant rate for long enough periods that the plume reaches a steady state entrainment of ambient fluid into the turbulent plume is assumed to occur at a rate proportional to the local velocity of the plume plume motion is considered in two dimensions one horizontal dimension perpendicular to the glacier front and the vertical dimension an integral model is formulated for the conservation equations of volume momentum buoyancy and sediment flux along the path of a turbulent plume injected into stably stratified ambient fluid sedimentation occurs from the plume when the radial component of the sediment fall velocity exceeds the entrainment velocity when the plume reaches the surface it is treated as a radially spreading surface gravity current for which exact solutions exist for the sediment deposition rate flocculation of silt and clay particles is modeled using empirical measurements of particle settling velocities in fjords to adjust the settling velocity of fine grained sediments sedplume has been applied to mcbride inlet alaska a temperate glaciated fjord where the majority of sedimentation originates from meltwater sources sedplume produces rates and patterns of sedimentation in good agreement with observations with calculated peak ice proximal annual sedimentation rates of approximately 22 m yr 1

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

the paths and timing of late paleozoic ice revisited new stratigraphic and paleo ice flow interpretations from a glacial succession in the upper itarare group parana basin brazil abstract this paper examines a glacial diamictite bearing succession from the upper itarare group taciba formation in eastern parana basin brazil the object of study provides the opportunity to investigate in detail the late stages of glacial sedimentation during the late paleozoic ice age lpia in this sector of sw gondwana with implications for glacial cyclicity and regional paleo ice flow reconstructions sedimentology geological mapping and palynological analysis allowed the recognition of four facies associations comprising subaqueous outwash mass transport tide influenced delta front and tide influenced delta plain deposits the succession records at least two episodes of ice margin advance and retreat into a marine influenced environment and can be placed in the earliest permian based on the palynomorph assemblage cross stratification in outwash facies and deltaic deposits indicate sediment transport to the sw the same revealed by deformational structures in mass transport diamictites derived from downslope resedimentation of glaciomarine sediments during deglaciation a glacial source to ne is therefore indicated and is in agreement with paleo ice flow directions obtained from previously studied localities to the north this north derived early permian glaciation contrasts with glacial sources to the se recognized in the lower and middle intervals of the itarare group the scenario suggests a geometric reconfiguration of the parana basin during the lpia and the migration of ice centers with time during the late paleozoic ice age in sw gondwana

deciphering the late cretaceous cenozoic structural evolution of the north peruvian forearc system the link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm this paper aims at deciphering the structural architecture and uplift history of the north peruvian forearc system to better understand the evolution and the mechanics that govern the late cretaceous cenozoic building of this active margin in this study we report surface structural geology data interpretation of seismic reflection profiles apatite fission track data and the construction of two offshore onshore crustal scale balanced cross sections the structure of the north peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust related structural highs involving continental oceanic basement rocks and off scrapped sediments the thrust systems bound thick thrust top forearc depocenters mainly deformed by crustal normal to strike slip faults and thin skinned gravitational instabilities the sequential restoration of the margin calibrated with apatite fission track data suggests a correlation between uplift shortening and plate convergence velocity during late cretaceous and miocene pliocene quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease the development of crustal normal to strike slip faulting and subsidence zones might be the consequence of slab flexure local basal erosion along subduction fault and or oblique subduction associated with sediment loading control we conclude that the evolution of the north peruvian forearc system was controlled by subduction dynamics strong sediment accumulation and recent ridge subduction and it recorded the orogenic loading evolution of the andes over the cenozoic

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

modern glacimarine processes and potential future behaviour of kronebreen and kongsvegen polythermal tidewater glaciers kongsfjorden svalbard

forearc basin formation in the tectonic wake of a collision driven coastwise migrating crustal block the example of the north andean block and the extensional gulf of guayaquil tumbes basin ecuador peru border area trench parallel extensional strain resulting from the northward drift of the north andean block has controlled the tectonic evolution of the gulf of guayaquil tumbes basin at least for the past 1 8 1 6 ma industrial multichannel seismic and well data document that e w to ene low angle detachment normal faults the posorja and jambeli detachment systems to the north and the tumbes detachment system to the south accommodated the main subsidence step along the shelf area during late pliocene quaternary times 1 8 1 6 ma to present two tectonic regimes showing different styles and ages controlled the evolution of the southern ecuador and northern peru continental margin and shelf the n s extensional regime along the shelf area is related to north andean block drift whereas the e w extensional regime along the continental margin results from tectonic erosion at depth strain rotation takes place along a major n s trending transfer system formed by the inner domito fault and the inner banco peru fault which bound the detachment systems to the west the strike slip component along this transfer system roughly located at the continental margin shelf break evolved as a response to slip along the detachment systems bounding the basin to the north and to the south the tumbes detachment system is the master fault controlling basin evolution through time and it may represent the shallower expression of a reactivated obduction megathrust it connects landward with the continental structures assumed to be part of the eastern frontier of the north andean block for the past 2 ma the total lengthening calculated along a complete n s transect of the gulf of guayaquil tumbes basin ranges between 13 5 and 20 km this lengthening is compatible with the documented drift of the north andean block for the same period of time the gulf of guayaquil tumbes basin is not a classical pull apart basin it exemplifies a particular type of pull apart basin basically controlled by 1 detachments extending downward across the brittle crust and 2 plate coupling along the subduction decollement which controls the inward segmentation of deformation

upper paleozoic glacigenic deposits of gondwana stratigraphy and paleoenvironmental significance of a tillite succession in northern victoria land antarctica abstract late paleozoic glacial deposits are widespread in gondwana in antarctica the best outcrops occur in the central transantarctic mountains ellsworth mountains pensacola mountains and in southern victoria land whereas they are rare and very scattered in northern victoria land which represents a linkage sector with tasmania and eastern australia the aim of the present research is to define the stratigraphic setting and the environmental interpretation of a poorly studied lower permian glacigenic succession located near orr glacier in the lanterman range in northern victoria land it has great importance because it represents the only significant glacigenic succession for this wide area marking and defining time and modality of a glacial postglacial transition during the early permian a critical time interval in the paleoenvironmental evolution of southern gondwana this succession named here as the lanterman formation lies directly on to crystalline basement and is overlain by a thick permian fluvial succession takrouna formation the results provided by sedimentological facies analysis and palynological analysis integrated with a limited petrographic characterization show a correlation framework between two isolated successions outlining their stratigraphic architecture and subdivided into a lower glacial portion and an upper postglacial portion the former asselian in age is dominated by diamictite sandstone mudstone with lonestones and carbonate deposits suggesting repeated advance and retreat of a terrestrial glacier with facies associations indicating environmental changes from subglacial to glaciofluvial to glaciolacustrine the latter is dominated by lacustrine mudstone with decreasing lonestones upward thin bedded sandstone conglomerate and a thick fluvial sandstone and pebbly sandstone succession at the top signalling the transition to a fluvial system through time the overall dataset suggests that the late paleozoic glacigenic deposits of northern victoria land record the evolution from a setting characterized by a terrestrial small ice cap that underwent repeated advances and retreats due to climate cycles in a lacustrine setting into a postglacial paleoenvironmental scenario with a wide fluvial system draining northwards from victoria land towards the tasmanian basin the results contribute to increasing knowledge of the timing and modalities of the late paleozoic ice age in gondwana particularly for polar regions such as antarctica

change of tectono stratigraphic regime in the australian plate during the 99 ma mid cretaceous and 43 ma mid eocene swerves of the pacific the clockwise bend at 99 ma mid cretaceous in linear volcanic chains in the tropical pacific coincides with a change from pre 99 ma head on chilean type subduction of the pacific plate beneath eastern gondwana to 99 43 ma sinistral oblique mariana type subduction and strike slip breakup by simple sea floor spreading between australia and antarctica and by backarc spreading in the southwest pacific the 99 ma breakup of australia from antarctica is documented by a mid cretaceous unconformity this tectono stratigraphic change founded modern australia with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south the counterclockwise bend at 43 ma mid eocene the emperor hawaiian bend coincides with the onset of structure in the challenger rift of new zealand the eromanga cooper basin of central australia and the oil shale grabens of coastal queensland

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

facies architecture and grounding line fan processes of morainal banks during the deglaciation of coastal maine submarine jet processes are inferred from glaciomarine facies exposed in gravel pits in southwestern coastal maine the geometry and distribution of fan facies depend on 1 the proximity to the grounding line and stream effluxes 2 the angle of jet trajectory from glacier conduits and 3 sediment remobilization processes syndepositional glaciotectonic deformation further augments morainal bank formation through pushing and squeezing of fan sediments at the grounding line complex process sediment interactions along the temperate tidewater margin of the laurentide ice sheet are recorded in the facies architecture of sedimentary sequences in morainal banks morainal bank accumulation was governed by rapid fluvial deposition and outwash jet dynamics that controlled the spatial distribution of sedimentary facies near the grounding line meltwater dynamics change rapidly where sediment laden fresh water is discharged at or near the sea floor turbulent mixing with ambient sea water and discharge fluctuations cause rapid changes in flow competence accompanied by the dumping of bed load gravel and sand at the apices of grounding line fans in the morainal banks jet trajectory relative to the morainal bank slope determines whether a jet will make contact with the morainal bank gravel and sand remain in bed load traction as long as the jet is in contact with the morainal bank bed load dumping and settling of the coarse suspended load occurs where buoyant forces in the jet overcome momentum forces or where the jet is deflected by the morainal bank below these buoyant jets backflow eddies can produce currents that drive ripple migration toward the grounding line abrupt facies changes record fluctuations in jet discharge and trajectory and sediment redistribution by sediment gravity flows initiated near the grounding line

slope instabilities at an active continental margin large scale polyphase submarine slides along the northern peruvian margin between 5 s and 6 s a mega submarine slide was evidenced along the peruvian margin during a seabeam survey of the r v charcot bourgois et al 1986 the debris slide was initially interpreted as the result of the slope failure occurring along a seaward curved scarp and extending from east to west along the line of maximum slope complementary bathymetrie data obtained from the r v sonne survey conducted to the north and to the south of the previous surveyed area has resulted in the identification of large scale polyphase submarine slides involving a total surface of about 1000 km2 between latitudes 5 15 s and 6 05 s using seabeam and hydrosweep multibeam echosounder data in combination with deep sea submersible observations three distinct slope failure types related to three main stages have been revealed the three sliding phases occurred roughly along the same trend orientated n230 and are therefore mainly controlled by the n80 orientation of the subducting nazca plate 1 the first phase of slope failure is documented by a debris avalanche deposit which extends from the lower slope down to 5 km within the trench floor the deposit originates from the northern wall of a wide valley located along the upper slope 2 the second phase of slope failure is characterized by a debris avalanche with a crescent shaped scar located along the middle slope and a hummocky deposit covering the lower slope and extending up to 10 km across the trench the volume of rock involved in this event is estimated to some 250 km3 the slope failure is assumed to be related to an oversteepening of the middle slope induced by a rollover deformation 3 the third phase of slope failure corresponds to a translational sliding block and a toppling block with volumes of 6 km3 and 13 km3 respectively the seismic energy produced during the seismic cycle has greatly increased facturation and fluids buildup along the area previously weakened by a rollover fold a restricted n s folding is observed in the vicinity of the trench to the north of the two debris avalanche deposits it may have formed in relation to the local compression limited to the subduction of the nazca plate sliding and folding thus document the paradox between the compressive regime in the lower plate and the extensional regime in the upper part of the upper plate

reconstruction off preglacial topography using a postglacial flooding surface upper paleozoic deposits central transantarctic mountains antarctica abstract upper paleozoic glacial deposits in the central transantarctic mountains are the basal deposits within a late paleozoic to early mesozoic basin that formed along the margin of the east antarctic craton this basin was a foreland basin throughout much of its history and was part of a larger scale basin that stretched across the paleo pacific margin of gondwanaland our reconstruction of the preglacial topography in the central transantarctic mountains suggests that deposition began within two topographic depressions located on top of eroded rocks of the lower paleozoic ross orogenic belt isopach paleocurrent and lithofacies data support such a hypothesis this interpretation implies that tectonic activity was not a factor in the formation of the depositional basin and that little r no tectonic activity was occurring along the adjacent continental margin during glacial deposition although glacial deposits are present all along the paleo pacific continental margin of antarctica and gondwanaland our findings suggest that initial sedimentation began within a series of discontinuous depocenters a flooding surface that separates upper paleozoic glacial deposits from overlying postglacial black shales in the central transantarctic mountains is used as a datum for reconstructing the preglacial topography the postglacial flooding surface resulted from flooding of the depositional basin following collapse of the gondwanide ice sheet results using this approach aided us in reevaluating the factors that controlled the formation of the depositional basin in antarctica and in determining the tectonic setting of the paleo pacific margin of antarctica during deposition of the upper paleozoic glacial rocks the use of a flooding surface as a datum is a technique that may be useful for reconstructing paleotopography in other settings

hardly used habitats dearth and distribution of burrowing in paleozoic and mesozoic stream and lake deposits limited use of substrate ecospace by a meager infauna in streams and lakes is indicated by analysis of more than 10 000 observations of bioturbation in permian through jurassic freshwater deposits in contrast marine substrates have been inhabited and bioturbated since the cambrian colonization of freshwater substrates differed fundamentally from that of marine substrates bioturbation enhanced flux of dissolved materials across the sediment water interface was not operating until after the paleozoic in freshwater ecosystems

50 million year long record of glacial to postglacial marine environments preserved in a carboniferous lower permian graben northern perth basin western australia abstract the perth basin is an intracratonic rift in western australia and contains a carboniferous to cretaceous infill in excess of 12 km thick some 2 km of mid carboniferous to lower permian glacially influenced marine strata spanning the serpukhovian to kungurian about 50 my form one of the longest late paleozoic cold climate successions preserved anywhere in gondwana and record the transition from full glacial to postglacial conditions at high 70 paleolatitudes the great thickness of the succession reflects an abundant supply of glaciclastic sediment from the adjacent ice covered yilgarn craton and continued subsidence along the darling urella fault system the oldest part of the basin fill comprises a 1 5 km thick succession of massive and laminated marine mudstones with striated dropstones nangetty formation deposited in a fiord like environment from plumes of suspended sediment dilute turbidity currents and icebergs meltwater inputs are recorded by erosionally based multistory channels filled with coarse grained gravity flow facies wicherina member deposited on a fan delta along the steep faulted basin margin the nangetty formation passes upward into a regressive succession of postglacial mudstones holmwood shale with bioclastic calcarenites and marine macrofossils capped by sandstone and mudstone facies high cliff sandstone deposited in a storm influenced inner shelf setting on the outer margins of coalesced fan deltas along the basin margin the overlying irwin river coal measures contain a flora that indicates colonization of fan deltas and the yilgarn craton by ferns and lycopods an overlying thick transgressive shale with ice rafted debris carynginia formation records renewed subsidence but continuing seasonally cool climates where coarse debris was rafted by ice into a marine embayment the sedimentology of the perth basin highlights the key role of glacial meltwaters in transporting coarse and fine grained clastic sediment to marine basins rather than direct glacial processes per se the equivalent terrestrial record of glaciation and climate change across the yilgarn craton at this time is very limited

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

along strike variations in the thermal and tectonic response of the continental ecuadorian andes to the collision with heterogeneous oceanic crust oblique to strike geological segmentation in the andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates as well as the upperplate expressions of differing along strike subducted slab age strength and composition we present new white mica and biotite 40 ar 39 ar and zircon and apatite fission track data from several traverses across the cordillera real of ecuador in the northern andes that reveal distinct along strike differences in the timing of accelerated crustal cooling during the cenozoic the data record elevated cooling rates from temperatures of v380 c during v65 55 and v43 30 ma from all sampled regions of the cordillera real and at v15 ma and since v9 ma in the northern cordillera real each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust elevated cooling rates of up to v30 20 c myr were initiated during the palaeocene and eocene early oligocene along the entire contemporaneous margin of ecuador and were driven by the accretion of the oceanic pallatanga terrane and pin on macuchi block respectively onto northwestern south america both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the caribbean plateau and accreted onto the margin during the approximately northeastward migration of the plateau into its current position within ecuador the development of higher topography and elevated cooling rates of up to 50 c myr at v15 ma and since v9 ma are restricted to the region north of 1 30ps and is situated above the postulated subducted flatslab section of the aseismic carnegie ridge plate convergence rate calculations suggest the carnegie ridge collided with the ecuador trench at v15 ma which caused the pre existing coastal provinces to displace to the northeast subsequently driving extension and marine ingressions in southern ecuador and compression and uplift in northern ecuador fl 2001 elsevier science b v all rights reserved

an origin for laminated glacimarine sediments through sea ice build up and suppressed iceberg rafting laminated glacimarine sediments are observed in visual core logs and x radiographs from scoresby sund and nansen fjord east greenland they are mostly underlain and overlain by massive or stratified glacimarine diamicton dmm or dms which is a product of iceberg delivery of heterogeneous debris and in scoresby sund reworking by deep drafted iceberg keels the laminated sediments are ams radiocarbon dated to two cold periods since the last late weichselian deglaciation the younger dryas stadial milne land stadial in east greenland and the little ice age during cold climatic events multiyear shorefast sea ice sikussak formed in these fjords and trapped the icebergs fine grained laminated muds fl were deposited in scoresby sund when the flux of icebergs was suppressed but turbid meltwater continued to provide some sediment flux to the fjord systems varying through time to produce laminations in nansen fjord thinner and often massive mud layers fm resulted from shorter intervals of sea ice cover with no ice rafting stratified diamicton layers dms which alternate with mud deposition to produce a laminated unit probably represent intervening times of more open conditions with iceberg rafting in scoresby sund foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition the absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites there is no evidence of macrofaunal activity and bioturbation is absent from the laminated sediments satellite data show that multiyear shorefast sea ice is present in several areas of the high arctic today and this traps icebergs calved from interior ice cap drainage basins thus the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and quaternary arctic