quaternary tectonic response to intensified glacial erosion in an orogenic wedge active orogens are thought to behave as internally deforming critical taper wedges that are in rough long term equilibrium with tectonic influx and erosional outflux spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation topography and deformation of orogens thereby affecting wedge taper however the impact of the most severe transition in northern hemisphere climate during the cenozoic era the onset of glaciation has hitherto not been empirically documented here we analyse the spatial patterns of denudation and deformation and their temporal variations in the heavily glaciated st elias orogen in southern alaska low temperature thermochronometry thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global scale intensification of glaciation in the middle pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf this led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment we propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics intense glaciation during the middle pleistocene epoch led to focused denudation and mass redistribution within the st elias orogen in southern alaska and resulted in structural reorganization of the orogen the tectonic response of this orogen to climate change is consistent with predictions of numerical models

seismic images of the transition fault and the unstable yakutat pacific north american triple junction in southern alaska the pacific plate and yakutat terrane subduct beneath the north american plate along the aleutian trench and pamplona zone respectively and are sliding past each other at minimal rates along the transition fault as the deformation front of the pamplona zone stepped eastward during the pliocene pleistocene the pacific north american yakutat triple junction became unstable four recent seismic images reveal that the transition fault changes from a single strike slip boundary east of the deformation front to three strands that step increasingly seaward between the deformation front and the aleutian trench the southern two strands deform the pacific crust and the outermost of these became increasingly convergent sometime since 1 ma as demonstrated by young growth strata we propose that this internal deformation of the pacific plate is an attempt to re attain stability which can only be reached by creating a tectonic boundary collinear with the pamplona zone the plate reorganization will result in initiation of subduction such that a portion of former pacific crust will become accreted to the north american plate such accretion events caused by triple junction instability may be an important mechanism for transferring oceanic crust to continental margins

gulf of alaska continental slope morphology evidence for recent trough mouth fan formation glaciated continental shelves are host to numerous morphologic features that help understand past glacier dynamics southeastern alaska is home to the st elias mountains an active orogen that also hosts temperate marine glaciers during glacial periods ice streams advance across the continental shelf carving shelf crossing troughs that reach the shelf edge we use high resolution multibeam data to develop the relationship between the yakutat and alsek sea valleys and the resulting continental slope morphology the shelf and slope geomorphology can be divided into statistical groupings that relate to the relative balance of erosion and deposition our analysis indicates that only the yakutat system has been able to build an incipient trough mouth fan the extreme sediment supply from this region was able to overwhelm the steep initial topography of the transform margin while further to the east sediment slope bypass dominates this analysis provides an extreme end member to existing studies of temperate glaciation along continental margins the unique interplay between rapid uplift due to ongoing collision and the massive erosion caused by temperate glaciers provides for sedimentary flux far above most other systems

submarine valleys in the northeastern gulf of alaska characteristics and probable origin abstract the continental shelf of the northeastern gulf of alaska between prince william sound and cross sound is cut by at least eight major valleys from west to east these are hinchinbrook seavalley egg island trough kayak trough bering trough pamplona troughs yakutat valley alsek valley and yakobi valley evidence common to most of these troughs or valleys indicating that the present morphology is due to glacial processes includes 1 a pre holocene subbottom erosional surface incised into the underlying lithified strata of the shelf 2 u shaped cross sections both at the sea floor and at the pre holocene erosional surface 3 concave longitudinal sections commonly shoaling at the seaward end 4 till like sediments collected from the walls or outer shelf adjacent to the troughs and 5 seismic stratigraphy that can be correlated with bottom samples indicative of glacially derived strata depressions with tens of meters of relief are present on the pre holocene subbottom erosional surface beneath most of these valleys these depressions have been partially filled by a seaward thinning wedge of holocene glacial flour clayey silt that is filling the valleys and blanketing the inner shelf at rates as high as 15 mm yr based on 210 pb measurements although glaciation played a dominant role in the modern morphology of these sea valleys structural features including structurally controlled topographic highs on the shelf e g tarr bank kayak island pamplona spur and fairweather ground influenced the flow directions of the glacial lobes

seismic stratigraphic evidence for glacial expanse during glacial maxima in the yakutat bay region gulf of alaska 1 modern shelf bathymetry bordering the gulf of alaska exhibits shelf crossing sea valleys that suggest focused pathways for ice flow during glacial conditions using an integrated seismic data set between the present yakutat and alsek sea valleys we investigate the glacial stratigraphic record in order to improve our understanding of the regional glacial system during maximum glacial conditions our investigations reveal four glacial unconformities of which the latter two are overlain by sediment packages hundreds of meters thick we suggest that these unconformities are indicative of ice advance phases during the little ice age lia the last glacial maxima lgm and two pre lgm advances with glacial retreat sequences preserved from the youngest two the advances were dominated by ice expanse from the malaspina glacial system and alsek river districts rather than the hubbard glacial system and only show distinctive morainal bank development near the shelf edge and near the mouth of or within modern bays fjords or river valleys this observation strongly supports rapid and continuous retreat from glacial maxima conditions during climatic warming all except the inferred lia sequence transgress the shelf and exhibit concentrated erosion in overdeepened troughs analogous to cross shelf troughs similar to those observed on other high latitude glaciated shelves the two alaskan troughs discussed here may be end member examples of high sediment flux systems due to the temperate glacial setting combined with an actively exhuming orogen

geophysical insights into the transition fault debate propagating strike slip in response to stalling yakutat block subduction in the gulf of alaska on the basis of faulting mapped on seismic reflection and bathymetric data seismicity current plate motions and evidence that the yakutat block may be anomalously thick we propose a tectonic model for yakutat pacific interactions including the often debated transition fault to the east deformation associated with the queen charlotte fairweather fault system is extending offshore facilitating westward propagation of strike slip motion along the eastern segment of the transition fault to the west the oblique slip pamplona zone and transition faults merge at an embayment in the continental margin where a north south dextral strike slip fault within the pacific plate illuminated by the 1987 1992 earthquake swarm intersects the pacific yakutat tectonic boundary these fault patterns are consistent with modern plate motions and reflect a plate boundary reorganization that may be caused by resistance to subduction by the yakutat block a possible moderate sized oceanic plateau

southern weddell sea shelf edge geomorphology implications for gully formation by the overflow of high salinity water 1 submarine gullies are the most common morphological features observed on antarctic continental slopes the processes forming these gullies however remain poorly constrained in some areas gully heads incise the continental shelf edge and one hypothesis proposed is erosion by overflow of cold dense water masses formed on the continental shelf we examined new multibeam echo sounder bathymetric data from the weddell sea continental slope the region that has the highest rate of cold dense water overflow in antarctica ice shelf water isw cascades downslope with an average transport rate of 1 6 sverdrups sv in the southern weddell sea our new data show that within this region isw overflow does not deeply incise the shelf edge the absence of gullies extending deeply into the glacial sediments at the shelf edge implies that cold high salinity water overflow is unlikely to have caused the extensive shelf edge erosion observed on other parts of the antarctic continental margin instead the gullies observed in the southern weddell sea are relatively small and their characteristics indicative of small scale slides probably resulting from the rapid accumulation and subsequent failure of proglacial sediment during glacial maxima

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

flow switching and large scale deposition by ice streams draining former ice sheets fast flowing ice streams are responsible for the bulk of mass transfer through large ice sheets we use extensive three dimensional seismic data from the western norwegian margin to explain how a several hundred kilometer long ice stream has undergone major switching in flow direction from one glaciation to the next the direction of ice flow is inferred from the pattern of buildup of thousands of cubic kilometers of glacier derived debris and observations of large scale streamlined landforms on former subglacial beds we demonstrate that ice streams can undergo major changes in flow direction through modification of their large scale topographic setting whereas ice stream switching in modern ice sheets has been regarded mainly as a reflection of internal changes in ice sheet dynamics switching over successive 100 k y glacial cycles may in this case be a response to the effects of continuing sediment deposition and the large scale development of ice influenced continental margins

seismic and gps evidence for the kinematics and the state of stress of active structures in south and south central tibetan plateau abstract since the middle miocene widely distributed n s striking rifts or rift depressions and ne nw striking strike slip faults have developed as major structures in southern and south central tibet active structures seismic mechanisms and directions and rates of movement determined from gps data are different in south and south central tibetan plateau in southern tibet n s striking normal faults and a few transtensional transpressional faults are the main structures but none of the gps measurements show eastward movement in south central tibet ne and nw striking transpressional transtensional faults and several large scale e w and wnw striking dextral and sinistral strike slip faults are the main structures and are consistent with the movement direction indicated by the gps data on the other hand the pattern of earthquake data from the south central tibetan plateau and especially from the eastern and western syntaxes are very complicated these structures may be produced by n s contraction which has resulted in the n s striking linear structures parallel to the direction of maximum compressive stress and conjugate ne and nw striking transpressional transtensional faults on the southern side of the qiangtang block and in the eastern and western syntaxes but the deformation is not continuous from the south to the south central tibetan plateau underthrusting of the indian plate under the southern tibetan plateau after the middle miocene may be the main cause of these structural features

ice sheets viewed from the ocean the contribution of marine science to understanding modern and past ice sheets over the last two decades marine science aided by technological advances in sediment coring geophysical imaging and remotely operated submersibles has played a major role in the investigation o

categorizing the morphologic variability of siliciclastic passive continental margins the basic morphology of the continental shelf slope and rise on passive continental margins has many variations in the modern ocean environment through using a satellite derived bathymetric data set of the global ocean we have developed a classification for the shape of modern siliciclastic dominated passive margins the classification subdivides 50 margins into five distinct shape categories based on each margin s pattern of sea floor slopes as a function of depth by comparing these shape categories with the underlying stratal architecture sediment input and present degree of canyon incision of the margins we find apparent correlations between these factors and basic margin shape in general gently sloped margins tend to occur in regions with high sediment input few modern canyons and unstable substrates higher gradient margins tend to have lower sediment input more modern canyons and a variety of subsurface architectures these results suggest two important conclusions 1 morphology differences among modern siliciclastic passive margins can be objectively and systematically categorized and 2 these shape differences seem to be related to aspects of the modern sedimentary environment despite the fact that the margins have evolved over geologic time

late cenozoic seismic stratigraphy and glacial geological development of the east greenland and svalbard barents sea continental margins abstract the european program on the late cenozoic evolution of the polar north atlantic margins ponam running from 1990 to 1994 resulted in a wealth of seismic data and sediment cores particularly from the svalbard and barents sea continental margin but also from areas of the east greenland margin deep sediment coring was undertaken on both margins during odp legs 152 and 162 this paper uses the ponam generated information as well as previous and subsequent seismic and core data to review our present understanding of the glacial geological development of these regions four main depositional facies have been identified these are represented by hemipelagic glaciomarine sediments sandy silty debris flows diamictic debris flows and tills deposited directly beneath grounded ice the temporal and spatial distribution of these four facies determines the architecture and seismic character of the two continental margins the two regions show significant differences with regard to both the timing of initial glaciation and the response of the ice sheets to climatic variability glacial deposition has taken place on the east greenland margin at least since 7 ma but apparently only since 2 5 ma on the svalbard barents sea margin significant glacial expansion across the continental shelf probably occurred in the early and late pliocene in east greenland whereas the glaciers on svalbard and the barents sea did not reach the shelf edge until the early pleistocene despite a shorter glacial period average glacial sedimentation rates are 2 3 times higher on the svalbard barents sea margin than on the studied parts of the east greenland margin the svalbard barents sea ice sheet has advanced and retreated much more frequently during the plio pleistocene than the greenland ice sheet glacial regime polar on greenland and polythermal to temperate in svalbard and the barents sea and the more easily erodible preglacial bedrock of svalbard and the barents sea are thought to be main factors responsible for the differences in ice sheet behavior and consequently glacial sediment production

evidence for multiple quaternary ice advances and fan development from the amundsen gulf cross shelf trough and slope canadian beaufort sea margin abstract the seismic stratigraphy and sedimentary architecture of the amundsen gulf trough and adjacent slope canadian beaufort sea margin are investigated using a grid of 2 d seismic reflection data the inner shelf of the amundsen gulf trough is interpreted to be composed predominantly of exposed or near surface bedrock overlain by a spatially discontinuous veneer of glacimarine to open marine sediment there is a seaward transition from exposed bedrock on the inner shelf to a thick up to 500 m outer shelf prograding wedge of acoustically semi transparent sediment eight seismic sequences divided into four megasequences are described from the outer shelf stratigraphy eight till sheets are identified from megasequences a to c providing evidence for at least eight quaternary ice stream advances through the amundsen gulf trough to the shelf break a trough mouth fan with a minimum volume of about 10 000 km 3 is present on the adjacent slope the amundsen gulf ice stream probably represented the most northwesterly marine terminating ice stream of the laurentide ice sheet through much of the quaternary providing a major route for ice and sediment transfer to the arctic ocean the youngest till sheet within the amundsen gulf trough megasequence d was probably deposited by a subsidiary ice stream the anderson ice stream subsequent to retreat of the last late wisconsinan amundsen gulf ice stream this provides evidence of dynamic ice sheet behaviour and the reorganisation of the northwest laurentide ice sheet margin during the last deglaciation a number of buried glacigenic landforms including palaeo shelf break gullies and a grounding zone wedge with a volume of 90 km 3 are described from the amundsen gulf trough stratigraphy lateral grounding zone wedges are identified at the northern and southern lateral margins of the amundsen gulf and m clure strait troughs respectively and are interpreted to have been formed roughly contemporaneously by ice streams in amundsen gulf and m clure strait

subglacial bedform evidence for a major palaeo ice stream and its retreat phases in amundsen gulf canadian arctic archipelago ascertaining the location of palaeo ice streams is crucial in order to produce accurate reconstructions of palaeo ice sheets and examine interactions with the ocean climate system this paper reports evidence for a major ice stream in amundsen gulf canadian arctic archipelago mapping from satellite imagery landsat etm and digital elevation models including bathymetric data is used to reconstruct flow patterns on southwestern victoria island and the adjacent mainland nunavut and northwest territories several flow sets indicative of ice streaming are found feeding into the marine trough and cross cutting relationships between these flow sets and utilising previously published radiocarbon dates reveal several phases of ice stream activity centred in amundsen gulf and dolphin and union strait a large erosional footprint on the continental shelf indicates that the ice stream ca 1000 km long and ca 150 km wide filled amundsen gulf probably at the last glacial maximum subsequent to this the ice stream reorganised as the margin retreated back along the marine trough eventually splitting into two separate low gradient lobes in prince albert sound and dolphin and union strait the location of this major ice stream holds important implications for ice sheet ocean interactions and specifically the development of arctic ocean ice shelves and the delivery of icebergs into the western arctic ocean during the late pleistocene copyright c 2006 john wiley sons ltd

timing and significance of glacially influenced mass wasting in the submarine channels of the greenland basin the most extensive systems of submarine channels on the continental margins of the norwegian greenland sea occur in the greenland basin 72 75jn geophysical records show that these channels are up to 100 m deep 4 km wide and extend for about 300 km from the middle continental slope off northeast greenland to the abyssal depths of the basin mass wasting deposits in the form of debris flows and turbidity currents as well as hemipelagic sediments dominate sediment cores recovered from the channels radiocarbon dates indicate that debris flow and turbidity current activity in the channels had ceased by 13 000 years bp and sedimentation rates show a corresponding order of magnitude decrease after this time masswasting in the submarine channels of the greenland basin therefore relates to full glacial and deglacial conditions this implies a more extensive late weichselian ice sheet in northeast greenland than traditionally thought the ice sheet extended onto the outer continental shelf and may have reached the shelf edge delivering debris and sediment laden meltwater onto the upper slope channel formation is most likely the product of turbidity current activity during successive glaciations of the northeast greenland continental shelf holocene sediments from the channel systems are predominantly of hemipelagic origin and formed in a low energy ice distal environment the low gradient 1j channels of the greenland basin are therefore a glacially influenced sedimentary system contrasts in slope morphology and sediment architecture between the greenland basin and trough mouth fans elsewhere in the norwegian greenland sea are not the result of variations in slope gradient rather these contrasts reflect the interplay between bedrock lithology of the continental shelf rates of sediment delivery sediment texture meltwater volume and relative size of ice sheet drainage basins

depositional and microfaunal response to pliocene climate change and tectonics in the eastern gulf of alaska abstract the yakataga formation provides an excellent record of pliocene paleoclimate in the gulf of alaska and northeastern pacific ocean evidence for glaciomarine influence and paleoclimatic change includes the distribution of ice rafted debris and diamictite planktic and benthic foraminiferal biofacies and variable sediment accumulation rates three paleoclimatically defined intervals within the pliocene yakataga formation are recognized in onshore and offshore sections interval p1 5 35 to 4 2 ma contains the first evidence of neogene glaciomarine deposition in the form of ice rafted debris and rare diamictite interval p2 4 2 to 3 0 3 5 ma exhibits a reduction in glaciomarine influence and warming to cool temperate conditions interval p3 3 0 3 5 to 1 8 ma contains massive amounts of glaciomarine diamictite and correlates with other evidence indicating the onset of major northern hemisphere glaciation sediment accumulation rate and foraminiferal based paleobathymetric curves show some correlation to the above paleoclimatic subdivision but also significant independent relationships indicating a strong tectonic influence on those parameters comparison of the yakataga record to odp sites in the north pacific shows that there is good agreement in the ice proximal yakataga and deep sea records of pliocene paleoclimate change

coupled stratigraphic and structural evolution of a glaciated orogenic wedge offshore st elias orogen alaska 1 the st elias orogen is the result of 10 myr of oblique convergence and flat slab subduction in the gulf of alaska between north america and the yakutat microplate extensive glaciation and a complex tectonic environment make this region a unique case study in which to examine the details of terrane accretion and the possible coupled influence of climate and tectonic drivers on the structural and topographic evolution of an orogenic wedge reflection seismic profiles across the offshore pamplona zone fold thrust belt the frontal st elias orogenic wedge provide constraints for quantifying pleistocene deformation recorded in the glaciomarine yakataga formation the total amount of pleistocene shortening observed varies from 3 to 5 mm yr compared to the current gps derived yakutat north america convergence rate across the st elias orogen of 45 mm yr growth strata and kinematic fold analysis allow comparison of relative timing of fault activity which reveals temporal and spatial shifting of active deformation during the glacial period faulting localized adjacent to the coastline and at the current submarine deformation front the abandoned currently inactive region is colocated with the major glacial depocenter in the region the bering trough these observations imply that glacial processes such as sediment loading and focused erosion during advance retreat cycles has a direct effect on the evolution of individual faults within the pamplona zone and the overall deformation pattern in the offshore st elias margin this information provides key constraints for understanding how climatic shifts may have affected the evolution of margin architecture during pleistocene glacial interglacial periods

outburst flooding and the initiation of ice stream surges in response to climatic cooling a hypothesis abstract outburst flooding from subglacial reservoirs and associated surging of ice streams are caused by processes following climatic cooling that produce ice shelf grounding on proglacial sills trapping subglacial water according to an hypothesis presented here glaciers often advance into proglacial water bodies cooling may allow ice shelf formation and advance causing grounding on a proglacial sill trapping subglacial water ice shelf freeze on to the sill and development of a local reversal in ice air surface slope over the sill then are likely allowing ice thickening and water overpressurization if basal thawing then occurs as is likely an outburst flood and a surge may be triggered these processes may have been involved in heinrich events generation of antarctic subglacial lakes and meltwater scouring of some regions

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages