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

long term fore arc basin evolution in response to changing subduction styles in southern alaska detrital zircon u pb and fission track double dating and hf isotopes from the mesozoic and cenozoic strata in the southern alaska forearc basin system reveal the effects of two different modes of flat slab subduction on the evolution of the overriding plate the southern margin of alaska has experienced subduction of a spreading ridge ca 62 50 ma and an oceanic plateau ca 40 0 ma when a subducting spreading ridge drives slab flattening our data suggest that after the ridge has moved along strike retro arc sediment sources to the forearc become more predominant over more proximal arc sources spreading ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent thin sedimentary strata in the forearc basin when a subducting oceanic plateau drives slab flattening our data suggest that basin catchments get smaller and local sediment sources become more predominant crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that combined create topography and increase rock exhumation rates consequently the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation the cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages this study demonstrates the merit of double dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large scale tectonic processes in magmatic regions

millennial scale temperature variations in north america during the holocene 1 a mean continental july temperature reconstruction based on pollen records from across north america quantifies temperature variations of several timescales for the past 14 000 cal yr bp in north america temperatures increased nearly 4 c during the late glacial reaching maximum values between 6000 and 3000 cal yr bp after which mean july temperatures decreased superimposed on this orbital scale trend are millennial scale temperature variations that appear coherent in structure and frequency with highresolution ice marine and other terrestrial paleoclimate records of the holocene during the holocene climate in north america appears to have varied periodically every 1100 years rather than the 1500 year cycle found during the last glacial period coherence at frequencies between 900 and 1100 years between land ice and ocean records suggests a common forcing associated with widespread surface impacts during the holocene these results provide important insight to the global warming debate as the observed twentieth century temperature increase appears unprecedented compared to our mean north american temperature reconstruction of the past 14 000 years

radiocarbon dating peatland development key steps in reconstructing past climate in the central appalachian mountains abstract canaan valley in west virginia contains a greater area of peatlands than any other locality in the mid atlantic highlands extensive fieldwork focused on peat stratigraphy combined with high resolution radiocarbon dating was used to evaluate five peatlands within canaan valley national wildlife refuge cvnwr one hundred soil cores were profiled and described 30 with laboratory analysis including 52 radiocarbon dates calibrated basal peat dates from the five peatlands indicate the onset of peat genesis ranged from 18 600 to 15 200 cal yr bp basal peat dates on the two oldest cores are 1800 to 2200 years older than published dates on peat initiation in any other appalachian mountain peatlands peat accumulation rates varied from 0 02 mm yr to 1 34 mm yr with a mean of 0 14 mm yr results of age depth profiles for six well dated cores consistently exhibit rapid accumulation during the late pleistocene heinrich stadial 1 bolling allerod interstadial and younger dryas cold stadial lower accumulation rates in the early holocene greenlandian age even lower accumulation rates during the mid holocene northgrippian age and the most rapid peat accumulation at the onset of the late holocene early meghalayan age a paucity of shallow peat dating younger than 2000 bp may reflect a reduction in peat accumulation or mixing of surface vegetation into near surface soil horizons soil cores from cvnwr suggest a somewhat different peat development history than the process of terrestrialization previously proposed for other peatland ecosystems in the region

intense localized rock uplift and erosion in the st elias orogen of alaska the st elias orogen in alaska is one of the world s highest coastal mountain ranges an age analysis of detrital material in active sediment systems in the inaccessible ice covered valley bottoms reveals localized exhumation that is driven by coupling between erosion and active tectonic rock uplift

peat accumulation in northern wetlands abstract mean long term rates of peat accumulation are higher in boreal and temperate peat deposits than in subarctic regions of canada although peatlands are extensive in the subarctic climatic change probably accounts for the development of southern peatlands during the middle to late holocene and for the late holocene decline in growth of many subarctic peat deposits in northwestern peat deposits peat of wet sphagnum lawns and treed wetlands tended to accumulate more rapidly than peat of sphagnum hummocks and sedge fens long term net rates of carbon accumulation in canadian peatlands typically range from 10 to 35 g c m2 yr

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

holocene climate variability and change a data based review the holocene thermal maximum with peak temperatures prior to 7 ka bp is mostly accentuated in the northern hemisphere still visible in the southern hemisphere and possibly did not exist in the tropics between this period and the modern warming a remarkable negative temperature trend occurred in the northern hemisphere which was probably the effect of a decreasing orbital induced insolation during the boreal summer on average the northern hemisphere humidity precipitation records do not show any significant trend a mechanistic explanation for the multi decadal to century scale holocene cold relapses which mainly occurred in the atlantic european regions exists for only the early holocene cooling events which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the laurentide ice sheet possibly the late holocene cold events after c 4 ka bp are influenced by the covarying influence of major tropical volcanic eruptions and grand solar minima

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

geologic evolution of the yukon river implications for placer gold abstract the greatest placer potential in northwest canada lies in preglacial drainage systems the largest placer gold deposits are associated with pliocene pre glacial fluvial gravels of the dawson range in particular klondike plateau of west central yukon the abundance and or the lack of gold concentration in this area were controlled by the ability of the streams to aggrade in response to changes caused by extensional faulting in the tintina trench differential uplift and regional denudation gold bearing gravels in the northern and eastern slopes of the dawson range are found in low order tributaries of the pre glacial south flowing yukon river glaciation played an important role in masking and changing the direction of drainage and creating new channels in this region the earliest known drainage changes relate to late miocene formation of the tintina trench and early pliocene uplift of the st elias mountains prior to these events the yukon river drained south into the gulf of alaska initial regional glaciation 2 6 2 9 ma diverted the southward drainage toward the northwest becoming part of the kwikhpak river in alaska the present yukon river drainage basin is about 27 5 larger than the ancestral kwikhpak river basin the evolution of the river is described here in three stages 1 drainage in pre late miocene 2 drainage in early pliocene and 3 drainage after earliest pliocene glaciation

current deformation in the northern canadian cordillera inferred from gps measurements 1 continuous and campaign style global positioning system gps measurements provide new constraints on the first order current deformation pattern of the northern cordillera of nw canada and eastern alaska the yakutat block is currently colliding with north america in the corner of the gulf of alaska our data infer that relative yakutat north america motion is accommodated across the eastern boundary by right lateral motion 40 mm a mainly on the fairweather fault and minor shortening 6 mm a to the north collision is taken up by shortening 31 mm a mainly on the chugach st elias fault system with westward extrusion and possible counterclockwise rotation of the yakutat block and alaskan fore arc facilitated by 23 mm a right lateral motion that is shared by several faults the seismicity pattern indicates that plate boundary deformation is far reaching producing strain throughout eastern alaska yukon and western northwest territories our gps data confirm the transfer of strain from the yakutat collision zone and enable the extent of plate boundary deformation to be mapped thereby defining the western edge of stable north america gps sites in sw yukon show motion of 3 10 mm a to the ne confirming that strain is transferred at least 400 km from the yakutat collision continued transfer north toward the mackenzie delta and ne to the mackenzie mountains indicated by current seismicity is not yet well resolved by the campaign gps data which are hampered by coseismic and postseismic effects of the 2002 mw 7 9 earthquake on the denali fault in eastern alaska

glacial and periglacial erosion of the appalachians abstract the marine 18 o record indicates that the first ice advance into the appalachians equivalent to that of the late wisconsin occurred in the pliocene at about 2 4 ma only periodic localized glacial and periglacial activity occurred in the northern appalachians from 2 33 to 0 85 ma after 0 85 ma middle to late pleistocene eight out of ten glaciations covered the northern appalachians and brought periglacial conditions to the southern appalachians during the last 850 000 years glaciation extended to the late wisconsin limit within the appalachians for 15 of the time and extended to the early wisconsin limit just north of the appalachians for 25 of the time pleistocene glacial erosion of the appalachians of 120 200 m is necessary to account for the estimated volume of pleistocene ocean sediment derived from the appalachians and the estimated volume of pliocene pleistocene glaciogenic ocean sediment derived from the entire laurentide ice sheet this amount of glacial erosion occurring over the maximum expectable duration of pliocene pleistocene ice cover of 247 000 years yields glacial erosion rates from 0 5 0 8 m ka 1 such depths of erosion by thick warm based ice streams were localized in the lowlands and estuaries of the northern appalachians in the maritimes the presence of thin cold based ice caused minimal erosion of uplands periglacial landforms and tundra boreal forest were distributed throughout the appalachian highlands and the northern coastal plain during the glacial maxima periglacial erosion of 0 15 0 30 m ka 1 near the ice in pennsylvania decline to 0 1 0 2 m ka 1 in the southern piedmont each cold period almost completely renewed the regolith by eroding slopes and filling valleys the cumulative effect of the eight to ten major cold events could have produced as much as a few ten s of meters of periglacial ridge top lowering during the pleistocene both estimated glacial and periglacial erosion rates greatly exceed estimated current fluvial erosion rates therefore glacial and periglacial processes should be considered the dominant processes in shaping the present appalachian landscape the northern appalachians may be evolving towards a form where the landscape provides just the shape necessary to permit the least work conveyance of the ice across the region during glacial maxima the southern appalachians may be evolving towards a form where the landscape provides just the hillslope form necessary to transport the debris provided by periglacial conditions

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

a three dimensional numerical simulation of typhoon holly in the northwestern pacific ocean 1 a three dimensional primitive equation model the princeton ocean model often called pom has been implemented for simulating typhoon holly generated in the tropical pacific ocean this is the first time that a study of this type previously used mostly for coastal regional simulations has been implemented for the northwestern pacific ocean from 24 n to 52 n including the east china sea the yellow sea and the east japan sea in the open ocean the model circulation sea surface elevation and temperature distribution with the passage of holly are described the results are in part compared with observation in the korea tsushima strait the model reproduces well several prominent features obtained in the observation such as a rapid increase of temperature in the korea strait during the passage of typhoon holly in august 1984 and reasonably explains how they happened around the vicinity of the typhoon center the model temperature field successfully presents sea surface cooling in the open ocean having been frequently observed in the past the model also suggests that a coastal jet around the korea strait and a cyclonic eddy field behind holly in the east china sea play an important role in the oceanic conditions although they have not yet been identified by observations

evolution of lithospheric strength after thrusting modeling of an eroding thrust belt indicates that immediately after thrusting the lithosphere is about twice as strong as unthickened cratonic lithosphere but after 10 to 20 m y it becomes weaker than cratonic lithosphere reaching a minimum of 40 to 70 of cratonic strength 30 to 100 m y after thrusting this may explain why rifting of thrust belts commonly occurs several tens of million years after thrusting ceases relative weakening results from 1 elevation of the geotherm caused by burial of radioisotope enriched surface rocks and 2 replacement of strong mantle rocks by weak crustal rocks in the lithospheric column low denudation rates enhance weakening by allowing radioisotope enriched rocks to remain buried longer our modeling indicates that 1 magmatism after thrusting is favored by high concentrations of heat producing elements in the lower plate and by slow denudation rates and 2 factors that affect denudation rate such as climate and the development of external drainage can significantly influence evolution of a thrust belt

tatla lake metamorphic complex an eocene metamorphic core complex on the southwestern edge of the intermontane belt of british columbia the tatla lake metamorphic complex tlmc which lies on the southwest side of the intermontane belt imb in british columbia has characteristics typical of a metamorphic core complex anticlinorial amphibolite grade gneissic and migmatitic core underlying a 1 to 2 5 km thick zone of mylonite and ductilely sheared metamorphic rocks which is in fault contact beneath an upper plate of low metamorphic grade cover rocks of the 1mb ductile shearing in the tlmc involved tonalitic to granodioritic orthogneiss and structurally overlying amphibolite grade metasedimentary rocks and greenschist grade chlorite actinolite albite schist structures observed throughout the ductilely sheared rocks include a gently dipping mylonitic foliation ss containing a mineral lineation ls which trends toward 280 100 20 minor folds of variable trend fs almost exclusively confined to metasedimentary rocks are interpreted as synductile shear vergence of these folds defines a movement sense and direction of top toward 290 20 kinematic indicators from rocks not deformed by synductile shear folds indicate a tops to the west sense of shear while those within metasedimentary rocks deformed by fs folds yield conflicting results with a tops to the west sense predominating calculated a directions from fs folds which deform ls lineations indicate nearly horizontal ds movement subparallel to 290 110 the entire metamorphic core of the tlmc has been deformed by upright west to west northwest trending shallowly plunging map scale folds f3 the steeply dipping northwest trending yalakom fault cuts all units and forms the southwestern margin of the tlmc u pb zircon geochronology has documented the existence of cretaceous 107 79 ma in the core and eocene 55 47 ma in the mylonitic zone deformation and metamorphism in the tlmc k ar dates for biotite and hornblende of 53 4 45 6 ma record the uplift and cooling of the tlmc during early and middle eocene time 55 47 ma metamorphic rocks of the tlmc were carried to higher crustal levels along the footwall of the tlmc normal ductile shear zone final uplift and development of f3 folds post 47 ma are possibly related to dextral motion along the yalakom fault the tlmc has structural style and timing of deformation similar to other metamorphic core complexes in southeastern british columbia local and regional evidence is consistent with the formation of the tlmc in a regional extensional setting within a vigorous magmatic arc similar interlayered gneisses with near horizontal layering and foliation may underlie the entire southern imb

vegetation and environment in eastern north america during the last glacial maximum abstract knowledge of the vegetation and environment of eastern north america during the last glacial maximum lgm is important to understanding postglacial vegetational and biogeographic dynamics assessing climate sensitivity and constraining and evaluating earth system models our understanding of lgm conditions in the region has been hampered by low site density problems of data quality particularly dating and the possibility that lgm vegetation and climate lacked modern analogs in order to generate improved reconstructions of lgm vegetation and environment we assembled pollen and plant macrofossil data from 21 and 17 well dated lgm sites respectively all sites have assemblages within the lgm timespan of 21 000 1500 calendar yr bp based on these data we prepared maps of isopolls macrofossil presence absence pollen analogs biomes inferred mean january and july temperatures and mean annual precipitation for the lgm tundra and open picea dominated forest grew along the laurentide ice sheet with tundra predominantly in the west in the east pinus dominated vegetation mainly p banksiana with local p resinosa and p strobus occurred extensively to 34 n and possibly as far south as 30 n picea glauca and a now extinct species p critchfieldii occurred locally picea dominated forest grew in the continental interior with temperate hardwoods quercus carya juglans liriodendron fagus ulmus growing locally near the lower mississippi valley at least as far north as 35 n picea critchfieldii was the dominant species in this region the florida peninsula was occupied by open vegetation with warm temperate species of pinus eastern texas was occupied by open vegetation with at least local quercus and picea extensive areas of peninsular florida and the continental interior had vegetation unmatched by any modern pollen samples the paleovegetational data indicate more extensive cooling in eastern north america at the lgm than simulated by either the ncar ccm0 or ccm1 climate models the occurrence of cool temperate conifers and hardwoods as far north as 34 35 n however indicates less severe cooling than some previous reconstructions paleoclimate inferences for the lgm are complicated by lowered atmospheric co 2 concentrations which may be responsible for the open nature and dominance of conifers in lgm vegetation

spatial extent of rapid denudation in the glaciated st elias syntaxis region se alaska 1 the ongoing collision of the yakutat terrane with the north american plate formed the st elias range in southeastern alaska previously published detrital zircon fission track dating of sand size material detected very rapid rock denudation within the syntaxis region of the st elias range but the size and spatial extent of the rapid exhumation are elusive due to the glacial cover that inhibits direct bedrock studies two possible mechanisms were suggested to explain the rapid denudation occurring underneath the seward malaspina glacier which differ in their spatial extent of rapidly exhumed rocks this study evaluates the spatial extent of rapid denudation at the st elias syntaxis region we investigate the cobble sized material of the malaspina glacier petrological classifications are used as a provenance tool and combined with zircon and titanite u th he analysis to reveal cooling rates of the glacial detritus in total 1998 cobbles are classified in the field petrographic characterization is conducted on 91 thin sections and the u th he ages of 59 cobbles are measured fourteen cobbles reveal young cooling ages of 3 2 ma originating from various lithologies of undeformed and deformed magmatic and metamorphic rocks older age populations peak at 12 27 and 36 ma the cooling ages and the mapped known extent of the different lithologies suggest that a larger then previously assumed area of the st elias syntaxis region experienced rapid exhumation rapid rock exhumation extends beyond the contact fault and comprises most of the seward malaspina glacier catchment

wave hindcast in the north pacific area considering the propagation of surface disturbances abstract ocean surface waves in the north pacific area are affected by storm winds it is necessary to consider the movement of storms to predict waves the impact of a time interpolation method for winds that considers the propagation of surface disturbances on ocean wave prediction from 2005 to 2006 in the north pacific area is demonstrated it is possible to interpolate surface winds even when there are multiple cyclones and anticyclones moving in different directions at different distances this method will be useful for wind fields with increasing amounts of spatial information the predicted wave heights and periods from the linearly interpolated winds and the winds predicted using this new method are compared with in situ observations from several moored buoys the predicted wave heights are also compared with those from several drifting buoys in the northwestern pacific the improvement of the wave height and period prediction is evident in the case where the difference in the predicted wave parameters between the linear interpolation and the present method is large the improvement of the wave height and period prediction is statistically significant at more than 95 in most cases it is shown that the wave height and period prediction can be improved by improving the time interpolation method however the improvement of the wave direction prediction is not evident

effect of long term wave climate variability on longshore sediment transport along regional coastlines abstract long term changes in wave climate have potential impacts on the evolution of regional coastlines this study investigates the impact of variable wave climate on the temporal dynamics of longshore sediment transport lst which plays a major role in defining the overall coastal geomorphology of regional coastlines the central west coast of india is considered as the study region era interim wave hindcast dataset over the period of 1979 2015 is used to derive the contemporary wave climate in this region the annual average significant wave height period and direction are computed and used to estimate lst of the study region this region experiences oblique waves from the w sw direction with an annual average significant wave height and wave period of 1 32 m and 8 10 s respectively that induces a gross northerly transport of approximately 450 000 m3 year it is found that the total lst is driven by swell waves and wind waves and shows a decreasing trend of about 5 over the analysis period the decay in lst is found to be linked with decreases in wave activity in this region the swell wave induced sediment transport is an order of magnitude higher than the wind wave induced lst it is observed that the swell generation in the lower latitudes has decreased resulting in reduced swell wave induced lst in the study area both swell and wind wave induced lst show seasonal variation finally a link is established between the seasonal variation of swell induced lst and the cyclogenesis periods in addition the wind wave induced lst is observed to have a direct link with the latitudinal position of the inter tropical convergence zone itcz

regional stratigraphy and structural setting of the kamloops group south central british columbia the kamloops group is redefined as an assemblage of lower to middle eocene volcanic and sedimentary rocks widespread in south central british columbia in the type area west of kamloops the basal

exhumation at orogenic indentor corners under long term glacial conditions example of the st elias orogen southern alaska abstract syntaxial bends in convergent plate boundaries or indentor corners display some of the most intriguing deformation patterns on earth and are type localities for aneurysms of coupled erosion thermal weakening and strain the st elias orogen in alaska is a small young convergent system that has been dominated by a glacial climate for much of its history and exhibits two prominent indentor corners that are not well understood we have added 40 new apatite u th he ages to the already extensive dataset for the low temperature cooling history of this orogen to constrain the pattern of exhumation in these indentor corners ages from the western syntaxis show minor variation across the structural hinge suggesting that the bend has little effect on the pattern of exhumation and that structures including the bagley fault connect smoothly from the orogen core to the subduction zone to the southwest rock uplift on the north flank of the range appears to increase steadily towards the eastern syntaxis which represents the apex in the right angle bend between a transform fault in the south and the collision zone in the west based on age elevation relationships zones of relative rock uplift can be defined in which the mt logan massif or the area just north of the eastern syntaxis experienced 4 8 km greater rock uplift than background levels northwest of the western syntaxis a bulge in relative rock uplift is symmetric about the hinge in the eastern indentor corner however rates of denudation in this bulge are not as rapid as the core of the fold and thrust belt and are lower than those implied by detrital cooling ages from beneath the seward glacier this implies that a large bull s eye of ultra rapid 5 mm yr exhumation does not occur and that the subpopulation of young detrital ages may be sourced from a narrow transpressional zone along the fairweather fault unlike the himalayan syntaxes it thus appears that an aneurysm of coupled erosion strain has not developed in either indentor corner of the st elias orogen this may indicate a limit to the degree to which glacial erosion can partition strain in convergent orogens similarly the likely existence of a through going dextral fault the totschunda fault through the eastern syntaxis implies that tectonics rather than surface processes exerts the main control on strain partitioning in these corners

late quaternary climate in the ridge and valley of virginia u s a changes in vegetation and depositional environment a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract browns pond virginia in the ridge and valley physiographic province contains a record of changing vegetational and depositional environments that dates to 17 130 bp six cores were retrieved in a transect of the pond pollen and macrofossils were identified from the longest central core and a series of ams radiocarbon dates obtained from identified macrofossils and sediment the pollen and macrofossil record combined with laterally consistent changes in lithostratigraphy reveal a changing climate from 17 300 to 14 100 bp a closed boreal forest of pinus picea abies grew at the site pinus dominates the pollen assemblage while picea and abies dominate the macrofossil assemblage subtle increases in more thermophilous and mesophytic taxa indicate gradual climate amelioration after the full glacial a marked increase in alnus at 14 100 bp signals an increase in moisture possibly related to the global evidence for rapid climate change at 14 000 bp at this central appalachian site abies and alnus are found in relatively greater amounts in the late glacial forest than previous studies indicated low organic contents and evidence of gleyed conditions seen in the core transect from 10 000 to 8000 bp point towards low water levels in the early holocene approximately coincident with the expansion of quercus

timing of late cenozoic tidewater glaciation in the far north pacific the onset of late cenozoic glacial events in the far north pacific ocean is recorded by ice rafted debris in the yakataga formation in the gulf of alaska the dating of these events is controversial ages based on molluscs suggest that initial late cenozoic tidewater glaciation occurred in the early middle miocene 15 16 ma previous work on planktic foraminifera indicates that this event is no older than late miocene probably latest miocene 5 6 ma resolution of this problem is important because the yakataga formation is the thickest most complete and best exposed repository of late cenozoic glaciomarine rocks in the northern hemisphere investigation of this record has broader implications for global temperature gradients paleoceanographic development of the far north pacific and northern hemisphere glacial history new planktic foraminiferal data from onshore and offshore yakataga formation sections in the gulf of alaska are compared to a regional depositional and chronostratigraphic framework in order to test whether the yakataga record is anomalous or consistent with the paleoclimatic record of the north pacific this comparison reconfirms that initial glaciomarine rocks of the yakataga formation are no older than late miocene new paleomagnetic data suggest that the base of the yakataga formation is within the lower gilbert polarity chron consistent with the planktic foraminiferal dating and k ar dates on glauconite correlation of the yakataga record to key offshore sections in the far north pacific deep sea drilling project dsdp sites 178 183 192 provides additional insights into the paleoclimatic significance of these rocks uplift of the alaska coastal ranges a necessary prelude to alpine glaciation occurred during late miocene time diatom biofacies dsdp sites 183 192 indicate warm middle miocene conditions climatic deterioration during the late middle and early late miocene time and initial tidewater glaciation between 5 0 and 6 7 ma a relatively warm mid pliocene interval succeeded this initial glaciation which was in turn followed by hemisphere scale glaciation beginning at 2 5 ma this second phase of yakataga glaciation may have begun as early as 3 0 3 5 ma glaciomarine rocks in the basal yakataga formation mark an important climatic event in the north pacific ocean they are latest miocene in age consistent with regional climatic information and not a middle miocene climatic anomaly

deformation during terrane accretion in the saint elias orogen alaska the saint elias orogen of southern alaska and adjacent canada is a complex belt of mountains formed by collision and accretion of the yakutat terrane into the transition zone from transform faulting to subduction in the northeast pacific the orogen is an active analog for tectonic processes that formed much of the north american cordillera and is also an important site to study 1 the relationships between climate and tectonics and 2 structures that generate large to great magnitude earthquakes the yakutat terrane is a fragment of the north american plate margin that is partly subducted beneath and partly accreted to the continental margin of southern alaska interaction between the yakutat terrane and the north american and pacific plates causes significant differences in the style of deformation within the terrane deformation in the eastern part of the terrane is caused by strike slip faulting along the fairweather transform fault and by reverse faulting beneath the coastal mountains but there is little deformation immediately offshore the central part of the orogen is marked by thrusting of the yakutat terrane beneath the north american plate along the chugach saint elias fault and development of a wide thin skinned fold and thrust belt strike slip faulting in this segment may be localized in the hanging wall of the chugach saint elias fault or dissipated by thrust faulting beneath a north northeast trending belt of active deformation that cuts obliquely across the eastern end of the fold and thrust belt superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen where the sedimentary cover of the yakutat terrane is accreted into the upper plate of the aleutian subduction zone these three structural segments are separated by transverse tectonic boundaries that cut across the yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the saint elias mountains onto the coastal plain the malaspina fault pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding onshore most of this boundary is buried beneath the western or agassiz lobe of the malaspina piedmont glacier the boundary between the central fold and thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the bering piedmont glacier

evidence for multiple episodic mid holocene hypsithermal recorded in two soil profiles along an alluvial floodplain catena southeastern tennessee usa abstract floodplain soil paleosol successions are valuable archives for reconstructing pleistocene holocene climate changes but have been relatively unstudied in the southern appalachian region two soil profiles on a small floodplain in southeastern tennessee usa were described and sampled in detail using both pedological and geological approaches including stable carbon isotope analysis of soil organic matter som correlation between the 2 profiles was constrained by uncalibrated ams 14c ages of bulk humates and using som 13c values both mobile and immobile elements four distinct 2 5 4 shifts towards less negative 13c values for som suggest 300 yr cyclicity and transient warmer and drier climate events with either water stressed c3 vegetation or as much as 35 c4 plants present during the mid holocene these postulated multi episodic drier climate conditions have never before been documented in the southern appalachian region and are tentatively correlated with mid holocene warming and drying in the eastern us the nearly time equivalent mid holocene events documented in texas the us high plains and in the gulf of mexico high rates of floodplain sediment accumulation 0 5 3 mm yr high clay content and maintenance of poorly drained soil conditions favor preservation of high resolution climate archives in floodplain deposits by inhibiting oxidation and translocation of organic c

characterizing large river history with shallow geophysics middle yukon river yukon territory and alaska abstract changes in longitudinal valley fill thickness can provide inferences about fluvial behaviour over millennia increased thickness of channel deposits may reveal climate induced accelerated sediment supply basin subsidence tectonic displacements or rising downstream base level decreases in thickness expressed as terraces may suggest active uplift decreased sediment flux or falling base level within a reach to date methods to characterize valley fills have depended largely on borehole data however recent developments in shallow geophysics make such investigations possible and provide a practical methodology to investigate alluvial rivers we carried out a longitudinal geophysical survey coupled with floodplain chronologies to characterize a 1000 km reach of the middle yukon river between western yukon territory and central alaska ground penetrating radar gpr and electrical resistivity ground imaging ergi profiles along the middle yukon river between central yukon and alaska coupled with channel bottom echo profiles demonstrates that there is little variation in thickness of gravel fill and depth of active scour holes gpr surveys near the white river the largest sediment source in the upper yukon show no significant longitudinal variation in gravel thickness 8 16 m up to near circle alaska 530 km of wandering channels geophysical profiles across the yukon flats sedimentary basin 430 km of braided and wandering channels show an increase in gravel thickness 25 30 m but this is consistent with compaction of underlying lacustrine sediment and maximum depths of contemporary scour holes from the western margin of the yukon flats to the dalton highway bridge 30 km confined valley with no floodplain or braid bars borehole data at the bridge indicates 6 10 m of gravel on bedrock beneath 3 6 m of water floodplain stratigraphy indicates there is little evidence of fluvial aggradation of the middle yukon during the holocene radiocarbon ages from the gravel overbank silt contact near present river level demonstrate a general vertical stability of the river with a period of rapid eolian accumulation during the late pleistocene and early holocene the consistency of gravel fill and scour hole depth and lack of holocene terraces along the 1000 km reach of the yukon indicate that the river has been in a state of mass balance equilibrium of sediment transport input output over the holocene despite massive sediment influxes from the glacial fed white river and crossing major faults variation in valley fill depth is not significant and further the yukon flats reach shows no evidence of bed aggradation during the pleistocene and has probably existed in equilibrium since the late pliocene

an extensive late cenozoic terrestrial record of multiple glaciations preserved in the tintina trench of west central yukon stratigraphy paleomagnetism paleosols and pollenthis is a companion paper to barendregt et al also in this issue geological survey of canada contribution 20100035 the tintina trench in west central yukon is a late miocene graben formed along the antecedent early tertiary tintina fault since its formation the trench has served as a sediment trap for alluvial and glacial deposits an extensive record of preglacial glacial and interglacial sediments spanning the late pliocene to late pleistocene has been preserved and is exposed today in modern landslide scars this sedimentary record comprises multiple sequences of tills outwash mudflows loess and paleosols the glacial sediments are the product of both local montane and regional cordilleran ice advances that channeled into the trench while loess and well developed paleosols brunisols and luvisols reflect nonglacial and interglacial conditions respectively the tintina trench exposures provide the most complete record of glaciations for the region paleomagnetism paleosols and palynology provide age constraints for the geological events a formal stratigraphic nomenclature is proposed for this region

horizontal variability of near inertial oscillations associated with the passage of a typhoon 1 surface currents to the east of okinawa island were observed by using hf high frequency ocean radars in august september 1995 during that period a typhoon passed near the observation area and the horizontal variability of near inertial oscillations associated with the typhoon passage was estimated in addition the near inertial amplitudes and horizontal wave number vectors were estimated these estimations showed that the near inertial amplitude was large in the offshore area and small near the coast the maximum near inertial wavelength was estimated to be in the order of 1000 km and the near inertial wave direction was southward and changed to northwestward on 23 august in 1995 a slab model incorporating low frequency currents was used to calculate near inertial currents it was found that the amplitude of calculated near inertial oscillations was also large in the offshore area moreover the phase propagation direction of the near inertial waves was southward and changed to northwestward or westward on 22 august the growth rate obtained from the dispersion relation was large in the offshore area where the near inertial amplitude was large

late holocene paleoecohydrology and carbon accumulation estimates from two boreal peat bogs in eastern canada potential and limits of multi proxy archives abstract the stratigraphy of four peat sequences collected in two peat bogs located in the eastmain river watershed 52 n 76 w james bay lowlands quebec canada was investigated to reconstruct past hydroclimatic conditions of peat accumulation and associated carbon dynamics during the late holocene analyses of macrofossils testate amoebae peat humification c n ratio and bulk density were performed at high resolution along each peat core allowing the potential of each proxy indicator under varying nutrient status and hydroclimatic conditions to be evaluated some synchronous changes were recorded both within and between peatlands suggesting the influence of allogenic factors in the development of these peatlands other reconstructed changes have highlighted autogenic succession processes related to the local geomorphic and hydrologic context highest peat carbon accumulation rates lorca were correlated with either wet conditions or high woody debris percentages suggesting that residence time of the biomass in the acrotelm and the nature of plant material can both influence carbon accumulation rates in peat bogs this study provides the first high resolution paleoecohydrological reconstructions from the mid boreal ecoregion of eastern canada a region in which peatlands occupy 30 to 60 of the land surface

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

late miocene to pleistocene source to sink record of exhumation and sediment routing in the gulf of alaska from detrital zircon fission track and u pb double dating

constraining the area of rapid and deep seated exhumation at the st elias syntaxis southeast alaska with detrital zircon fission track analysis the chugach st elias orogen southeast alaska southwest yukon formed in response to the ongoing yakutat microplate subduction collision with the north american plate due to heavy glaciation the region is a prime location to study active convergent orogenesis and climate tectonic interactions this study focuses on the long term distribution of deformation in the st elias syntaxis area where dextral motion along the plate bounding fairweather fault transitions into convergence we present 2718 new zircon fission track single grain ages from 26 glaciofluvial outwash samples the grain ages range from 293 ma to 0 2 ma and each sample contains two to five age populations with peaks between 267 64 ma and 1 2 0 7 ma 1 the rocks of the yakutat microplate are dominated by latest cretaceous and eocene fission track ages while the rocks of the north american plate in the syntaxis region reveal two exhumation phases at 5 1 ma and 2 7 ma the spatial pattern of 5 ma cooling ages shows that the area of rapid and deep exhumation at the st elias syntaxis is more extensive than previously known and confined to the south by the fairweather fault to the west by the seward glacier catchment and to the east possibly by the inferred connector fault the area seems to be 4800 km2 large and may extend farther to the north the new zircon fission track data further suggest a transpressional plate boundary since 30 ma and the onset of plate collision 15 12 ma

evidence for early glaciation of southeastern beringia between the klondike plateau and yukon tanana highlands of yukon and alaska respectively current maps explain glaciated alpine locales and periglacial areas in terms of localized pliocene pleisto

thermotectonic history of mt logan yukon territory canada implications of multiple episodes of middle to late cenozoic denudation abstract the extreme relief of the st elias mountains including mt logan is suggestive of a young mountain belt new apatite fission track data indicate that the mt logan massif experience rapid low temperature cooling during three distinct periods during the middle eocene middle miocene and pliocene each cooling episode the magnitude of which varies due to temporal variations in recorded paleogeothermal gradients can be tentatively linked to a tectonic cause eocene cooling may be due to re equilibration of isotherms following normal faulting caused by a combination of thermal weakening of the crust and a decrease in regional compressional stress due to the 43 ma change in relative motions between the pacific and north american plates the cause of miocene cooling is problematic and could reflect denudation in response to initial underplating of the yakutat terrane or a recorded change in heat flow unrelated to denudation pliocene cooling reflects erosion due to surface uplift that produced the spectacular present day topography of the st elias mountians this surface uplift is probably related to the coeval significant change in relative motion between the north american and pacific plates and or resistance to subduction by the yakutat terrane

cooling history of the st elias syntaxis southeast alaska revealed by geochronology and thermochronology of cobble sized glacial detritus

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

continental scale landscape evolution a history of north american topography the generation and evolution of continental topography are fundamental geologic and geomorphic concerns in particular the history of landscape development might contain useful information about the spatiotemporal evolution of deep earth processes such as mantle convection a significant challenge is to generate observations and theoretical predictions of sufficient fidelity to enable landscape evolution to be constrained at scales of interest here we combine substantial inventories of stratigraphic and geomorphic observations with inverse and forward modeling approaches to determine how the north american landscape evolved first stratigraphic markers are used to estimate postdepositional regional uplift present day elevations of these deposits demonstrate that 2 km of long wavelength surface uplift centered on the colorado rocky mountain plateaus occurred in cenozoic times second to bridge the gaps between these measurements an inverse modeling scheme is used to calculate the smoothest spatiotemporal pattern of rock uplift rate that yields the smallest misfit between 4 161 observed and calculated longitudinal river profiles our results suggest that cenozoic regional uplift occurred in a series of stages in agreement with independent stratigraphic observations finally a landscape evolution model driven by this calculated rock uplift history is used to determine drainage patterns denudation and sedimentary flux from late cretaceous times until the present day these patterns are broadly consistent with stratigraphic and thermochronologic observations we conclude that a calibrated inverse modeling strategy can be used to reliably extract the temporal and spatial evolution of the north american landscape at geodynamically useful scales

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

long term glacial erosion of active mountain belts example of the chugach st elias range alaska an emerging paradigm that equates glaciers to buzz saws of exceptional erosional efficiency has been strengthened by short term 10 2 yr sediment yields from southern alaska new low temperature cooling ages from this area the glaciated chugach st elias mountains constrain long term 10 6 yr exhumation rates vertically averaged exhumation rates reach 3 mm yr but are an order of magnitude lower than rates based on short term sediment yields whereas these exhumation rates are not exceptional for oro genic belts denudation patterns are strongly correlated with the distribution of glaciers and erosion appears to keep pace with con vergence and uplift these findings imply a coupling between gla cially dominated erosion and tectonics

periglacial geomorphology of the appalachian highlands and interior highlands south of the glacial border a review abstract many features reported in the appalachian region have been assigned a paleoperiglacial origin based on field relationships and their similarities with analogs active in present day actuoperiglacial environments these forms include but are not limited to sorted and nonsorted varieties of patterned ground grezes litees block fields block slopes and block streams cryoplanation terraces and hillslope and river terrace landscapes although very small scale features generally less than 1 m in plan or section dimension and some larger forms on steep hillslopes are known to be at least sporadically active today the large scale features discussed here are interpreted as either inactive or truly fossil periglacial phenomena thus they hav implications for paleoclimatic reconstruction and significance as indicators of relative landscape stability since the time s of their development this paper briefly reviews the historical dimension of early researchs work present selected examples of recent results and gives authors conclusions

a 1200 km long eocene metamorphic plutonic belt in the northwestern cordillera evidence from southwest yukon distinctive regional eocene metamorphic plutonic units of the coast belt in southwestern yukon match similar units in southeastern alaska and british columbia and possibly in the eastern alaska range and together form a belt originally 1200 km long the final high grade metamorphic event in the aishihik and kluane assemblages between the ruby range batholith and the denali fault zone occurred in latest paleocene to early eocene time structural petrologic and geochronologic evidence indicates that metamorphism occurred during a major period of west southwest vergent deformation and metamorphism the final phase of consumption of the kula plate at 43 ma may be linked to the culmination of metamorphism intrusion and deformation along the early cenozoic cordilleran margin

pollen response surface estimates of late quaternary changes in the moisture balance of the northeastern united states abstract quantitative estimates of late quaternary climate in the northeastern united states are reconstructed from fossil pollen data to evaluate changes in the regional moisture balance inferred from water level fluctuations we use environmental response surfaces to calibrate modern pollen data for 17 different taxa to an index of effective soil moisture and mean annual precipitation we apply these response surfaces to fossil pollen data from 60 sites in the region to reconstruct changes in soil moisture and mean annual precipitation at 3000 yr intervals from 12 000 yr b p to present the mapped reconstructions of soil moisture and mean annual precipitation illustrate how the regional moisture balance of the northeast may have changed over the last 12 000 yr in response to changing climate reconstructions of annual precipitation show a gradual increase from 30 below modern values at 12 000 yr b p to near modern values by 6000 yr b p and then remain relatively constant thereafter reconstructed changes in the index of effective soil moisture however show a pattern of near modern values at 12 000 6000 and 3000 yr b p with significantly lower values estimated for 9000 yr b p the time of maximum pine pollen abundances in the northeast this pattern of change is similar to the change in regional moisture balance inferred from stratigraphic records of water level fluctuations these results confirm previous interpretations based on records of water level fluctuations that conditions in the northeast were significantly drier during the early to middle holocene than at other times during the last 12 000 yr

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

volcanism in an arc transform transition zone the stratigraphy of the st clare creek volcanic field wrangell volcanic belt yukon canada the st clare creek volcanic field in the southwestern yukon overlies a tectonic transition in the wrangell volcanic belt between subduction to the northwest in alaska and transform faulting along the duke river fault in the southeast two large polygenetic volcanic centres dominated the miocene landscape of the st clare creek field the 18 16 ma wolverine centre and the 16 10 ma klutlan centre the wolverine centre evolved from a small alkaline shield volcano at 18 ma from which alkaline basalts hawaiites and mugearites erupted to a larger composite volcano between 18 and 16 ma composed of transitional basalt basaltic trachyandesite trachyte and rhyolite lavas and pyroclastic rocks the youngest wolverine lavas are calc alkaline basaltic andesites andesites and hybrid lavas transitional calc alkaline this temporal progression from alkaline through transitional to calc alkaline volcanism is accompanied by a systematic increase in the degree of silica saturation and decrease in fe si nb y and

crustal scale structural architecture shortening and exhumation of an active eroding orogenic wedge chugach st elias range southern alaska 1 active mountain building associated with the accretion of the yakutat microplate yt in southern alaska is characterized through the combination of a new balanced cross section and new low temperature cooling ages this analysis constrains the amount and timing of shortening the spatial and temporal trends of exhumation and the interplay between structural development and exhumation a fold and thrust belt comprising three principal thrust sheets the hope creek sullivan and an offshore thrust sheet from north to south characterizes the yt internal structure which has absorbed a minimum of 82 km shortening assuming shortening and foreland basin development occurred contemporaneously the shortening rate across the yt is 13 14 mm a after 5 6 ma detrital apatite fission track ages from south to north are unreset along the southern edge of the sullivan thrust sheet at the coast are reset and have ages younger than 6 3 ma within the thrust belt and have reset cooling ages of 13 ma in the north american upper plate only the zircon samples from the northern internal yt are potentially reset exhumation rates within the thrust belt vary from 0 3 0 1 mm a to 4 1 8 mm a combining the thermochronometric and structural data indicate that wedge exhumation since 6 ma is 500 km2 and that particle trajectories have larger horizontal than vertical components whereas exhumation and shortening have been focused on the windward side of the chugach st elias range since 6 ma the cooling ages do not uniquely distinguish between orographically versus tectonically controlled erosion

multiple episodes of cenozoic denudation in the northeastern brooks range fission track data from the okpilak batholith alaska the northeastern brooks range of alaska is a complex mesozoic to cenozoic northward verging fold and thrust belt in response to regional compression shortening in the upper crust has occurred thr

architecture kinematics and exhumation of a convergent orogenic wedge a thermochronological investigation of tectonic climatic interactions within the central st elias orogen alaska abstract the kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate but little research has been devoted to the long term effects of glacial erosion on orogenesis here we use low temperature apatite and zircon u th he and fission track thermochronometry along with subsidiary structural relationships and seismicity to develop a new architectural model of the st elias orogen in southern alaska which is one of the best examples of a glaciated orogenic wedge worldwide these data illustrate that the orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding thin skinned fold and thrust belt on the windward flank a structure beneath the bagley ice field separates these distinct deformational domains which we propose is a backthrust that makes the orogen doubly vergent thermochronometry within the orogenic wedge suggests that denudation and deformation are strongly influenced by glacial erosion long term exhumation at rates of up to 4 mm yr is concentrated within a narrow zone along the windward flank where glacier equilibrium lines intersect the orogenic wedge the onset of enhanced glaciation also coincided with a marked acceleration in exhumation across the orogenic wedge accelerated backthrust motion and a major shift in deformation away from the north american yakutat terrane suture chugach st elias fault we propose that accelerated glacial erosion forced the redistribution of strain along the backthrust and an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation which in turn are systematically truncated by the backthrust this focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially dominated orogen

cooperation among tectonic and surface processes in the st elias range earth s highest coastal mountains investigations of tectonic and surface processes have shown a clear relationship between climate influenced erosion and long term exhumation of rocks numerical models suggest that most orogens are in a transient state but observational evidence of a spatial shift in mountain building processes due to tectonic climate interaction is missing new thermochronology data synthesized with geophysical and surface process data elucidate the evolving interplay of erosion and tectonics of the colliding yakutat microplate with north america focused deformation and rock exhumation occurred in the apex of the colliding plate corner from 4 to 2 ma and shifted southward after the 2 6 ma climate change the present exhumation maximum coincides with the largest modern shortening rates highest concentration of seismicity and the greatest erosive potential we infer that the high sedimentation caused rheological modification and the emergence of the southern st elias intercepting orographic precipitation and shifting focused erosion and exhumation to the south

100 000 year long terrestrial record of millennial scale linkage between eastern north american mid latitude paleovegetation shifts and greenland ice core oxygen isotope trends abstract we document frequent rapid strong millennial scale paleovegetation shifts throughout the late pleistocene within a 100 000 yr interval 115 15 ka of terrestrial sediments from the mid atlantic region mar of north america high resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages ranging between two endmembers subtropical oak tupelo bald cypress gum forest and high boreal spruce pine forest sedimentary textural evidence indicates fluvial paludal and loess deposition and paleosol formation representing sequential freshwater to subaerial environments in which this record was deposited its total age depth model based on radiocarbon and optically stimulated luminescence ages ranges from terrestrial oxygen isotope stages ois 6 to 1 the particular core sub interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several greenland ice cores interstades gi2 to gi24 ois2 5 d this site thus provides the first evidence for an essentially complete series of dansgaard oeschger climate events in the mar these data reveal that the 100 000 yr preceding the late glacial and holocene in the mar of north america were characterized by frequently and dynamically changing climate states and by vegetation shifts that closely tracked the greenland paleoclimate sequence

late pleistocene and holocene climate and geomorphic histories as interpreted from a 23 000 14c yr b p paleosol and floodplain soils southeastern west virginia usa abstract field micromorphological pollen whole soil xrf and stable isotope geochemical methods were used to evaluate the latest pleistocene to holocene climate record from a floodplain terrace system in southeastern west virginia a late pleistocene 22 940 150 14 c yr b p silt paleosol with low chroma colors formed from fluviolacustrine sediment deposited during the last glacial maximum wisconsinan and records a cooler full glacial paleoclimate fluvial gravel deposited between the latest pleistocene and earliest holocene prior to 6360 40 14 c yr b p was weathered in the middle holocene under warmer drier climate conditions possibly correlated with the hypsithermal and altithermal events of the eastern and southwestern united states respectively the glacial to interglacial climate shift is recorded by 1 changes from a poorly drained landscape with fine textured soil characterized by high organic c and redoximorphic features related to fe removal and concentration to a well drained coarse textured setting without gley and with significant argillic bt horizon development 2 changes from a high zr and ti silt dominated parent material to locally derived coarse fluvial gravels lower in zr and ti 3 a shift from dominantly conifer and sedge pollen in the paleosol to a modern oak hickory hardwood assemblage and 4 a shift in 13 c values of soil organic matter from 28 to 24 pdb suggesting an ecosystem shift from cooler c3 dominated flora to one that was mixed c3 and c4 but still predominantly composed of c3 plants a root restrictive placic horizon developed between the late pleistocene silt paleosol and the overlying fluvial gravel because of the high permeability contrast between the two textures of soil materials this layer formed a barrier that effectively isolated the pleistocene paleosol from later holocene pedogenic processes

holocene peat and carbon accumulation rates in the southern taiga of western siberia abstract although recent studies have recognized peatlands as a sink for atmospheric co2 little is known about the role of siberian peatlands in the global carbon cycle we have estimated the holocene peat and carbon accumulation rate in the peatlands of the southern taiga and subtaiga zones of western siberia we explain the accumulation rates by calculating the average peat accumulation rate and the long term apparent rate of carbon accumulation lorca and by using the model of clymo 1984 philosophical transactions of the royal society of london series b 303 605 654 at three key areas in the southern taiga and subtaiga zones we studied eight sites at which the dry bulk density ash content and carbon content were measured every 10 cm age was established by radiocarbon dating the average peat accumulation rate at the eight sites varied from 0 35 0 03 to 1 13 0 02 mm yr 1 and the lorca values of bogs and fens varied from 19 0 1 1 to 69 0 4 4 g c m 2 yr 1 the accumulation rates had different trends especially during the early holocene caused by variations in vegetation succession resulting in differences in peat and carbon accumulation rates the indirect effects of climate change through local hydrology appeared to be more important than direct influences of changes in precipitation and temperature river valley fens were more drained during wetter periods as a result of deeper river incision while bogs became wetter from our dry bulk density results and our age depth profiles we conclude that compaction is negligible and decay was not a relevant factor for undrained peatlands these results contribute to our understanding of the influence of peatlands on the global carbon cycle and their potential impact on global change

sedimentary proxy evidence of a mid holocene hypsithermal event in the location of a current warming hole north carolina usa a wetland deposit from the southern appalachian mountains of north carolina usa has been radiocarbon dated and shows continuous deposition from the early holocene to the present non coastal records of holocene paleoenvironments are rare from the southeastern usa increased stable carbon isotope ratios 13c of sedimentary organic matter and pollen percentages indicate warm dry early to mid holocene conditions this interpretation is also supported by n alkane biomarker data and bulk sedimentary c n ratios these warm dry conditions coincide with a mid holocene hypsithermal or altithermal documented elsewhere in north america our data indicate that the southeastern usa warmed concurrently with much of the rest of the continent during the mid holocene if the current warming hole in the southeastern usa persists during a time of greenhouse gas induced warming elsewhere it will be anomalous both in space and time

crustal stabilization through the processes of ridge subduction examples from the chugach metamorphic complex southern alaska a tectonic process commonly overlooked in the growth and formation of continental crust is ridge subduction this process can stabilize a forearc accretionary complex through high grade metamorphism anatexis pluton emplacement and underplating of mafic rock an excellent example of the process is in the chugach metamorphic complex cmc southern alaska formed as a result of late cretaceous to paleogene subduction of the kula farallon or kula resurrection ridge ridge subduction subjected the trench fill turbidites of the accretionary prism to greenschist to amphibolite grade metamorphism under high temperature low pressure conditions converting them to a gneissic basement in the core of the cmc and regional near trench plutonism in addition to high grade metamorphism and near trench plutonism the cmc experienced three distinct phases of deformation associated with triple junction position in the process of becoming stabilized continental crust 1 accretionary prism related compression and metamorphism 2 eastward migration of the triple junction and associated ridge subduction producing orogen parallel extension peak metamorphism and mafic underplating and 3 dextral transpression following the migrating triple junction this combination of progressive deformation and tectonic phases produces continental crust effectively becoming a stable tectonic backstop by the time of neogene yakutat terrane collision the present day locus of deformation

low temperature thermochronology of the yakutat plate corner st elias range alaska bridging short term and long term deformation abstract this study investigates the long term deformation and rock exhumation of the subducting yakutat microplate corner at the st elias syntaxis region with a special focus on the area east and west of yakutat bay where major coseismic surface uplift occurred during a mw 8 2 earthquake in 1899 we use low temperature thermochronology to quantify the long term activity of thrust and reverse faults we present new apatite and zircon u th sm he ages from 35 bedrock samples collected along profiles crossing major faults that compose a one sided flower structure at the northern end of the fairweather fault the cooling ages reveal that rapid rock exhumation is accommodated by the eastern esker creek fault and the yakutat fault with rates of 2 3 mm yr and slower rates of

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

a stable isotope record of late cenozoic surface uplift of southern alaska abstract although the timing of an acceleration in late cenozoic exhumation of southern alaska is reasonably well constrained as beginning 5 6 ma the surface uplift history of this region remains poorly understood to assess the extent of surface uplift relative to rapid exhumation we developed a stable isotope record using the hydrogen isotope composition d of paleo meteoric water over the last 7 ma from interior basins of alaska and yukon territory our record which is derived from authigenic clays dclay in silicic tephras documents a 50 60 increase in d values from the late miocene 6 7 ma through the plio pleistocene transition 2 3 ma followed by near constant values over at least the last 2 ma although this enrichment trend is opposite that of a rayleigh distillation model typically associated with surface uplift we suggest that it is consistent with indirect effects of surface uplift on interior alaska including changes in aridity moisture source and seasonality of moisture we conclude that the dclay record documents the creation of a topographic barrier and the associated changes to the climate of interior alaska and yukon territory

climatic and human controls on holocene floodplain vegetation changes in eastern pennsylvania based on the isotopic composition of soil organic matter abstract a paleoenvironmental time series spanning the holocene was constructed using 29 radiocarbon ages and 149 standardized 13 c som values from alluvial terrace profiles along the middle delaware river valley there is good agreement between increasing 13 c som and panicoideae phytolith concentrations suggesting that variations in c 4 biomass are a major contributor to changes in the soil 13 c a measurement error deconvolution curve over time reveals two isotope stages ii i with nine sub stages exhibiting variations in average 13 c som average c 4 stage ii 10 7 4 3 ka shows above average 13 c som increase c 4 values with evidence of an early holocene warming and dry interval sub stage iib 9 8 8 3 ka that coincides with rapid warming and cool dry abrupt climate change events sub stage iid 7 0 4 3 ka is an above average 13 c som increase c 4 interval associated with the mid holocene warm dry hypsithermal the stage ii i shift at 4 3 ka documents a transition toward below average 13 c som decrease c 4 values and coincides with decreasing insolation and hydroclimatic change sub stages ib and id above average c 4 coincide with the first documented occurrence of maize in the northeastern usa and a substantial increase in human population during the late woodland these associations suggest that people influenced 13 c som during the late holocene

numerical modeling and field evidence of coastal overwash in southern new england from hurricane bob and implications for paleotempestology 1 in this paper we examine the use of coastal overwash modeling in conjunction with geological proxy techniques to provide a more comprehensive tool for paleotempestology southern new england which lies in the path of north tracking hurricanes has been a prime location for paleotempestological studies hurricane bob of 1991 is the most recent landfall in this region and has the most comprehensive data for model assessment and validation using the hurricane track central pressure and radius of maximum wind as input a collection of four interoperable model components simulates the meteorological conditions astronomical tides and storm surge ocean and coastal waves and the surf zone processes and runup onto dry land the computed surface pressure winds waves and water levels give very good agreement with data from weather stations moored buoys and tide gauges near the track and in the zone of maximum wind the validated wave conditions and storm water levels define the boundary conditions for coastal overwash modeling and the results show strong correlation with aerial photographs and sedimentary records at five sites near the landfall the results provide modern analogs for the interpretation of early hurricane landfalls in southern new england that lack an instrumental record reconstruction of paleohurricanes will require geological proxy data at multiple locations for the multivariate inverse analysis with uncertain paleotopography and storm characteristics

changes in the north pacific wave climate since the mid 1990s since the mid 1990s ocean wave reanalysis and in situ wave observations have revealed marked downward trends in wave height exceeding 0 1 m per decade in the midlatitude north pacific the wave period in the tropical pacific is also on a downward trend exceeding 0 4 s per decade during this period these changes in wave climate in the pacific are attributable to recently strengthened trade winds and la nina like conditions in the tropical pacific the downward trend in significant wave height in the midlatitude north pacific is due to strengthening of the negative phase of the pacific north american teleconnection numerical experimentations with a wave model also showed that the downward trend in the wave period in the eastern equatorial pacific was induced not only by increased wind waves due to strengthened trade winds but also by weakened propagating swells from the midlatitude north pacific

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

the thermochronological record of tectonic and surface process interaction at the yakutat north american collision zone in southeast alaska we investigate the material fluxes in space and time as a result of exhumation and erosion processes at the ongoing yakutat north american collision in southeast alaska many thermochronologic studies using a variety of sampling strategies are challenged by the widespread ice cover that limit field observations and accessibility this paper reviews new and published low temperature thermochronological data from southeast alaska to give a comprehensive interpretation of the exhumation patterns through time and how they are influenced by surface processes and climate change we find that the southeastern margin of alaska was exhumed and eroded long before the late miocene pliocene yakutat collision but since the beginning of the subduction of the yakutat lithosphere in the oligocene early miocene today there is a distinct pattern of exhumation in southeast alaska with a localized very rapid and deep seated exhumation at the yakutat plate corner st elias syntaxis where strike slip motion changes to convergence exhumation is also rapid but less deep along the dextral fairweather fault and in the evolving fold and thrust belt we present a re interpretation of the exhumation pattern in the fold and thrust belt and suggest that mass transport by exhumation is parallel to the observed active thrust faults and oblique to the suture zone and orogenic strike the locus of most rapid exhumation migrated from northwest to southeast with recent exhumation occurring near the st elias syntaxis exhumation of the chugach terrane rocks is still active however to a lesser degree than on the south side of the orogen where precipitation rates are much higher the wrangellia terrane to the north has experienced little exhumation and has essentially formed the backstop for terrane accretion in southeast alaska since the early cretaceous apatite u th he ages give the first evidence that rocks of the wrangell range have only been recently uplifted and eroded as a consequence of the continuing yakutat collision in general the thermochronology in southeast alaska reveals that climate variations across the region as well as changes through time have a limited influence on the pattern of erosion and that the location of deep exhumation is primarily influenced by tectonic processes

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

source to sink evaluation of sediment routing in the gulf of alaska and southeast alaska a thermochronometric perspective in this study we present a source to sink evaluation of sediment routing at the glaciated convergent margin in southeast alaska we investigate the efficacy of thermochronology to record spatial and temporal exhumation patterns in synorogenic sediment using neogene strata drilled by integrated ocean drilling program expedition 341 in the gulf of alaska we present 1641 and 529 new detrital zircon and apatite fission track ages respectively from strata deposited on the continental shelf slope and deep sea fans these data are compared to results from the proposed source terrains including the st elias mountains and new data from the alsek river we find that the offshore bagley bering sediment contains grains recording cooling ages much older 80 35 ma than those reported from the st elias syntaxis 3 2 ma indicating that extreme rapid exhumation does not extend west of the seward bagley divide data from the sediment on the continental shelf slope and proximal deep sea all yield similar results suggesting the same general source region since 1 2 ma and limited sediment mixing along this glaciated margin data from sediment in the distal deep sea show that extreme rapid and deep seated exhumation was ongoing at 11 8 ma overall this study demonstrates the strengths and limitations of using detrital fission track thermochronology to understand sediment routing on a glaciated convergent margin and to record changes in exhumation rates over geologic time scales